Method of operating water electrolysis and electricity generating system

ABSTRACT

A method of operating a water electrolysis and electricity generating system includes, at a time of switching from the water electrolysis mode to the electricity generating mode, a water electrolysis stopping step, a purging step and an electricity generation starting step. In the purging step after the water electrolysis stopping step, an oxygen-containing gas is caused to flow from an oxygen-containing gas flow path to a first gas-liquid separator via an oxygen-containing gas introduction flow path, a first supply flow path, a first inlet port member, a first fluid flow path, a first outlet port member, and a first lead-out flow path. In the electricity generation starting step after the purging step, the cell member is caused to generate electricity based on a predetermined required load value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2021-056088 filed on Mar. 29, 2021, thecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method of operating a waterelectrolysis and electricity generating system.

Description of the Related Art

For example, in JP 2015-191846 A, a water electrolysis and electricitygenerating system equipped with a cell member is disclosed. The cellmember includes an MEA (membrane electrode assembly), a first fluid flowpath, and a second fluid flow path. The MEA includes an electrolytemembrane, and a first electrode and a second electrode that sandwich theelectrolyte membrane therebetween. The first fluid flow path is a flowpath through which water and an oxygen-containing gas are supplied tothe first electrode. The second fluid flow path is a flow path throughwhich hydrogen gas is supplied to the second electrode. Such a waterelectrolysis and electricity generating system is capable of switchingbetween a water electrolysis mode and an electricity generating mode. Inthe water electrolysis mode, the water electrolysis and electricitygenerating system electrolyzes the water supplied to the firstelectrode, and thereby causes a product hydrogen gas to be generated atthe second electrode. In the electricity generating mode, the waterelectrolysis and electricity generating system generates electricity byan electrochemical reaction that takes place between theoxygen-containing gas supplied to the first electrode and the hydrogengas supplied to the second electrode.

SUMMARY OF THE INVENTION

In the aforementioned water electrolysis and electricity generatingsystem, it is desirable that the system can smoothly and reliably carryout switching between the water electrolysis mode and the electricitygenerating mode.

The present invention has the object of solving the aforementionedproblems.

One aspect of the present invention is characterized by a method ofoperating a water electrolysis and electricity generating systemcomprising a cell member having an MEA in which an electrolyte membraneis sandwiched between a first electrode and a second electrode, a firstfluid flow path configured to supply water and an oxygen-containing gasto the first electrode, and a second fluid flow path configured tosupply hydrogen gas to the second electrode, wherein the waterelectrolysis and electricity generating system is capable of beingswitched between a water electrolysis mode, in which the water suppliedto the first electrode is electrolyzed to thereby generate producthydrogen gas at the second electrode, and an electricity generatingmode, in which electricity is generated by an electrochemical reactionthat takes place between the oxygen-containing gas supplied to the firstelectrode and the hydrogen gas supplied to the second electrode, thewater electrolysis and electricity generating system further comprises asupply flow path connected to an inlet port member that communicateswith the first fluid flow path, a lead-out flow path connected to anoutlet port member that communicates with the first fluid flow path andfrom which a gas-containing water containing the product hydrogen gas isled out at the time of the water electrolysis mode, a water introductionflow path through which the water is introduced into the supply flowpath, an oxygen-containing gas flow path through which theoxygen-containing gas flows, an oxygen-containing gas introduction flowpath which introduces the oxygen-containing gas that flows through theoxygen-containing gas flow path into the supply flow path, and agas-liquid separator that separates into a gas and a liquid thegas-containing water that is guided from the lead-out flow path, themethod of operating the water electrolysis and electricity generatingsystem comprising, at a time of switching from the water electrolysismode to the electricity generating mode, a water electrolysis stoppingstep of stopping the water electrolysis by the cell member, after thewater electrolysis stopping step, a purging step of causing theoxygen-containing gas to flow from the oxygen-containing gas flow pathto the gas-liquid separator via the oxygen-containing gas introductionflow path, the supply flow path, the inlet port member, the first fluidflow path, the outlet port member, and the lead-out flow path, and afterthe purging step, an electricity generation starting step of causing thecell member to generate electricity based on a predetermined requiredload value.

Another aspect of the present invention is characterized by a method ofoperating a water electrolysis and electricity generating systemcomprising a cell member having an MEA in which an electrolyte membraneis sandwiched between a first electrode and a second electrode, a firstfluid flow path that supplies water and an oxygen-containing gas to thefirst electrode, and a second fluid flow path that supplies a hydrogengas to the second electrode, wherein the water electrolysis andelectricity generating system is capable of being switched between awater electrolysis mode, in which the water supplied to the firstelectrode is electrolyzed to thereby generate product hydrogen gas atthe second electrode, and an electricity generating mode, in whichelectricity is generated by the electrochemical reaction that takesplace between the oxygen-containing gas supplied to the first electrodeand the hydrogen gas supplied to the second electrode, the waterelectrolysis and electricity generating system further comprises a waterintroduction flow path which supplies the water to an inlet port memberthat communicates with the first fluid flow path, a lead-out flow pathconnected to an outlet port member that communicates with the firstfluid flow path and from which a gas-containing water containing theproduct hydrogen gas is led out at the time of the water electrolysismode, and a gas-liquid separator, which is formed to be capable ofstoring the water therein together with the water introduction flow pathbeing connected thereto, and to gas-liquid separate the gas-containingwater that is guided from the lead-out flow path, wherein the method ofoperating the water electrolysis and electricity generating systemcomprises, at a time of switching from the electricity generating modeto the water electrolysis mode, an electricity generation stopping stepof stopping the generation of electricity by the cell member, and awater electrolysis starting step of starting water electrolysis at thecell member in the case that the water level inside the gas-liquidseparator is greater than or equal to a lower limit level.

According to the one aspect of the present invention, by the purgingstep, the water (residual water) existing in the supply flow path andthe first fluid flow path of the cell member at the time of the waterelectrolysis mode can be drained into the first gas-liquid separator bythe oxygen-containing gas. Consequently, it is possible to smoothly andreliably carry out switching from the water electrolysis mode to theelectricity generating mode. Further, since a portion of the supply flowpath is used as the water supply flow path and the purge flow path, thewater electrolysis and electricity generating system can be made smallerin scale, together with enabling a reduction in the manufacturing costof the system.

In accordance with the another aspect of the present invention, sincewater electrolysis is initiated in the case that the water level in thegas-liquid separator is greater than or equal to the lower limit level,it is possible to suppress mixing of air into the water that is suppliedto the first fluid flow path of the cell member at the time of the waterelectrolysis starting step. Consequently, it is possible to smoothly andreliably carry out switching from the electricity generating mode to thewater electrolysis mode.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings, in which apreferred embodiment of the present invention is shown by way ofillustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a water electrolysis andelectricity generating system and a hydrogen station according to anembodiment of the present invention;

FIG. 2 is a schematic configuration explanatory diagram of the waterelectrolysis and electricity generating system shown in FIG. 1 ;

FIG. 3 is a cross-sectional explanatory view with partial omission of acell member shown in FIG. 2 ;

FIG. 4 is a block diagram of a system ECU shown in FIG. 2 ;

FIG. 5 is a flowchart illustrating a water electrolysis mode of thewater electrolysis and electricity generating system;

FIG. 6 is an explanatory diagram of operations in the water electrolysismode;

FIG. 7 is an explanatory diagram of switching between dehumidificationperformed by a first dehumidifying adsorption unit and a seconddehumidifying adsorption unit;

FIG. 8 is a flowchart illustrating an electricity generating mode of thewater electrolysis and electricity generating system;

FIG. 9 is an explanatory diagram of operations in the electricitygenerating mode;

FIG. 10 is a flowchart illustrating switching from the waterelectrolysis mode to the electricity generating mode;

FIG. 11 is a flowchart illustrating a purging step shown in FIG. 10 ;

FIG. 12 is an explanatory diagram of operations in the purging step;

FIG. 13 is a flowchart illustrating an electricity generationpreparatory step shown in FIG. 10 ;

FIG. 14A is a flowchart illustrating switching from the electricitygenerating mode to the water electrolysis mode;

FIG. 14B is a flowchart illustrating an electricity generation stoppingstep shown in FIG. 14A; and

FIG. 15 is a flowchart illustrating a water electrolysis preparatorystep shown in FIG. 14A.

DESCRIPTION OF THE INVENTION

A water electrolysis and electricity generating system 10 according toan embodiment of the present invention is a system that produceshydrogen gas using electrical power (surplus electrical power) such asrenewable energy or the like, and generates electricity using thehydrogen gas in the case that electrical power is required. As shown inFIG. 1 , the water electrolysis and electricity generating system 10 isconnected, for example, to a hydrogen station 400 via a low pressurehydrogen pipeline 402.

The hydrogen station 400 comprises a water electrolysis system 404, ahydrogen pressure boosting system 406, and a hydrogen tank 408. Thewater electrolysis system 404 produces hydrogen gas by electrolyzingwater using electrical power in the form of renewable energy or thelike. The hydrogen pressure boosting system 406 raises the pressure ofthe hydrogen gas produced by the water electrolysis system 404, andstores the hydrogen in the hydrogen tank 408. Hydrogen gas (includingbyproduct hydrogen gas) manufactured and transported from anotherfactory or the like may be stored in the hydrogen tank 408.

The low pressure hydrogen pipeline 402 supplies the hydrogen gas storedin the hydrogen tank 408 of the hydrogen station 400 or the hydrogen gasproduced by the water electrolysis system 404 to the water electrolysisand electricity generating system 10. Further, the low pressure hydrogenpipeline 402 supplies the hydrogen gas (hydrogen gas that has notaccumulated) produced by the water electrolysis and electricitygenerating system 10 to the hydrogen pressure boosting system 406 inorder to be stored in the hydrogen tank 408. The low pressure hydrogenpipeline 402 also functions as a tank for storing the hydrogen gas.Stated otherwise, in the present embodiment, the hydrogen tank 408 andthe low pressure hydrogen pipeline 402 function as a hydrogen storageunit 410.

As shown in FIG. 2 , the water electrolysis and electricity generatingsystem 10 comprises a cell member 12, a first device 14, a second device16, and a cooling device 18.

As shown in FIG. 3 , the cell member 12 includes a stack in which aplurality of cells 20 are stacked. Each of the cells 20 includes an MEA22 (membrane electrode assembly), and a first separator 24 and a secondseparator 26 sandwiching the MEA 22 therebetween. The MEA 22 includes anelectrolyte membrane 28, a first electrode 30, and a second electrode32. The first electrode 30 is arranged on one surface 28 a of theelectrolyte membrane 28. The second electrode 32 is arranged on anothersurface 28 b of the electrolyte membrane 28. The electrolyte membrane28, for example, is a solid polymer electrolyte membrane (cationexchange membrane). Such a solid polymer electrolyte membrane, forexample, is a thin membrane of perfluorosulfonic acid containing water.

The first electrode 30 includes a first electrode catalyst layer 34 anda first gas diffusion layer 36. The first electrode catalyst layer 34 isbonded to one surface 28 a of the electrolyte membrane 28. The first gasdiffusion layer 36 is laminated on the first electrode catalyst layer34. The second electrode 32 includes a second electrode catalyst layer38 and a second gas diffusion layer 40. The second electrode catalystlayer 38 is bonded to another surface 28 b of the electrolyte membrane28. The second gas diffusion layer 40 is laminated on the secondelectrode catalyst layer 38.

The first electrode catalyst layer 34 includes, for example, porouscarbon particles on which a platinum alloy is supported on surfacesthereof. The porous carbon particles are uniformly coated together withthe ion conductive polymer binder on the surface of the first gasdiffusion layer 36. The second electrode catalyst layer 38 includes, forexample, porous carbon particles on which a platinum alloy is supportedon surfaces thereof. The porous carbon particles are uniformly coatedtogether with the ion conductive polymer binder on the surface of thesecond gas diffusion layer 40. The first gas diffusion layer 36 and thesecond gas diffusion layer 40 include carbon paper or carbon cloth orthe like.

The first separator 24 and the second separator 26 are formed bypress-forming a thin metal plate to have a corrugated cross-sectionalshape. The thin metal plate, for example, is a steel plate, a stainlesssteel plate, an aluminum plate, or a plated steel plate. The thin metalplate may be a stainless steel plate on which a surface treatment forprotection against corrosion has been implemented, or an aluminum plateon which a surface treatment for protection against corrosion has beenimplemented. The first separator 24 and the second separator 26 arejoined to each other by a plurality of non-illustrated bonding lines tothereby form a joint separator 42.

A surface 24 a of the first separator 24 facing toward the MEA 22includes a first fluid flow path 44. A surface 26 a of the secondseparator 26 facing toward the MEA 22 includes a second fluid flow path46. A coolant flow path 48 through which a coolant flows is locatedbetween the surface 24 b of the first separator 24 and a surface 26 b ofthe second separator 26 that are joined to each other. The coolant flowpath 48 is formed by overlapping a rear surface shape of the firstseparator 24 in which the first fluid flow path 44 is formed and a rearsurface shape of the second separator 26 in which the second fluid flowpath 46 is formed.

As shown in FIG. 2 , an electrolytic power source 50, which is a DCpower source, is electrically connected to the cell member 12. The waterelectrolysis and electricity generating system 10, which is equippedwith such a cell member 12, is capable of switching between a waterelectrolysis mode and an electricity generating mode (fuel cell mode).In the water electrolysis mode, the water electrolysis and electricitygenerating system 10 electrolyzes the water supplied to the firstelectrode 30, and thereby causes a product hydrogen gas to be generatedat the second electrode 32. In the electricity generating mode, thewater electrolysis and electricity generating system 10 generateselectricity by an electrochemical reaction that takes place between theoxygen-containing gas supplied to the first electrode 30 and thehydrogen gas supplied to the second electrode 32. Although detailedillustration thereof is omitted, the electrical power generated by thecell member 12 is used, for example, for charging a non-illustratedbattery or the like. Moreover, the electrical power generated by thecell member 12 may be converted into AC power and supplied to a systempower supply network.

An impedance measurement unit 52 and a cell voltage measurement unit 54are attached to the cell member 12. The impedance measurement unit 52measures a DC resistance component of the cell member 12 from the cellvoltage, by energizing the first electrode 30 and the second electrode32 with a non-illustrated AC power source. The cell voltage measurementunit 54 measures the cell voltage of each of the cells 20 at the timethat electricity is generated.

A first inlet port member 56 a, a first outlet port member 56 b, asecond inlet port member 58 a, a second outlet port member 58 b, acoolant inlet port member 60 a, and a coolant outlet port member 60 bare installed in the cell member 12. The first inlet port member 56 aand the first outlet port member 56 b communicate with the first fluidflow path 44 of the cell member 12 (refer to FIG. 3 ). The first inletport member 56 a and the first outlet port member 56 b are connected tothe first device 14. At the time of the water electrolysis mode, wateris supplied from the first device 14 to the first inlet port member 56a. At the time of the electricity generating mode, the oxygen-containinggas is supplied from the first device 14 to the first inlet port member56 a. At the time of the water electrolysis mode, a gas-containingwater, in which there is contained the product hydrogen gas andbyproduct oxygen, is led out from the first fluid flow path 44 into thefirst outlet port member 56 b. At the time of the electricity generatingmode, an oxygen containing exhaust gas in which generated water iscontained is led out from the first fluid flow path 44 into the firstoutlet port member 56 b.

The second inlet port member 58 a and the second outlet port member 58 bcommunicate with the second fluid flow path 46 of the cell member 12(refer to FIG. 3 ). The second inlet port member 58 a and the secondoutlet port member 58 b are connected to the second device 16. At thetime of the water electrolysis mode, nothing is supplied from the seconddevice 16 to the second inlet port member 58 a. At the time of theelectricity generating mode, the hydrogen gas is supplied from thesecond device 16 to the second inlet port member 58 a. At the time ofthe water electrolysis mode, a product hydrogen gas in which water iscontained is led out from the second fluid flow path 46 into the secondoutlet port member 58 b. At the time of the electricity generating mode,a hydrogen exhaust gas in which water is contained is led out from thesecond fluid flow path 46 into the second outlet port member 58 b.

The coolant inlet port member 60 a and the coolant outlet port member 60b communicate with the coolant flow path 48 of the cell member 12 (referto FIG. 3 ). The coolant inlet port member 60 a and the coolant outletport member 60 b are connected to the cooling device 18.

The first device 14 comprises a pure water supply unit 62, a watercirculation unit 64, an oxygen-containing gas device 66, and a heatexchange device 68. The pure water supply unit 62 includes a watersupply flow path 70 in order to supply water (pure water) to the watercirculation unit 64. A municipal water supply valve 72, a pure waterproduction unit 74, a pure water regulating valve 76, and a check valve78 are installed in the water supply flow path 70 sequentially in thisorder from an upstream side toward the water circulation unit 64.

The municipal water supply valve 72 is an opening/closing valve thatopens and closes the water supply flow path 70. The municipal watersupply valve 72 adjusts the amount of municipal water supplied to thepure water production unit 74. Although not shown in the drawings, thepure water production unit 74 produces pure water, for example, bycirculating the municipal water through an activated carbon filter, anion exchange resin (ion exchange resin column), and a hollow fiberfilter. The pure water regulating valve 76 is an opening/closing valvethat opens and closes the water supply flow path 70. The pure waterregulating valve 76 adjusts the amount of the pure water produced by thepure water production unit 74 that is supplied to the water circulationunit 64. The check valve 78 permits the flow of the pure water from thepure water production unit 74 to the water circulation unit 64, andblocks the flow of the fluid from the water circulation unit 64 to thepure water production unit 74.

The water circulation unit 64 comprises a first gas-liquid separator 80,a water introduction flow path 81, a first supply flow path 82, and afirst lead-out flow path 84. The water introduction flow path 81 isconnected to the first gas-liquid separator 80. The first supply flowpath 82 connects the water introduction flow path 81 and the first inletport member 56 a to each other. The first lead-out flow path 84 connectsthe first outlet port member 56 b and the first gas-liquid separator 80to each other.

The first gas-liquid separator 80 separates into a gas and a liquid thefluid that is led out from the cell member 12. More specifically, at thetime of the water electrolysis mode, the first gas-liquid separator 80separates into a gas and a liquid the gas-containing water that is ledout from the first outlet port member 56 b of the cell member 12.Further, at the time of the electricity generating mode, the firstgas-liquid separator 80 separates into a gas and a liquid the oxygencontaining exhaust gas that is led out from the first outlet port member56 b of the cell member 12. Furthermore, at the time of the electricitygenerating mode, the first gas-liquid separator 80 separates into a gasand a liquid the hydrogen exhaust gas that is guided from the secondoutlet port member 58 b via the second device 16.

The first gas-liquid separator 80 includes a first storage unit 86 thatis capable of storing water. Pure water is supplied to the first storageunit 86 from the pure water supply unit 62. Further, the water, whichhas been separated from the fluid that is led out from the cell member12, is stored in the first storage unit 86. Therefore, mixed water, inwhich there are mixed the pure water that is guided from the pure watersupply unit 62 and the water that has been separated from the fluid thatis led out from the cell member 12, is stored in the first storage unit86.

The first storage unit 86 includes a partition wall 88 that partitions amore upper side than the water surface inside the first storage unit 86into a first chamber 86 a and a second chamber 86 b. The partition wall88 is separated from a bottom surface of the first storage unit 86. Aportion of the partition wall 88 is immersed in the water inside thefirst storage unit 86. Water is introduced from the water supply flowpath 70 into the first chamber 86 a of the first storage unit 86. Thefluid that is led out from the cell member 12 is introduced into thesecond chamber 86 b of the first storage unit 86.

In the first gas-liquid separator 80, a gas component of the fluid thatis guided to the second chamber 86 b is guided within the water (betweenthe partition wall 88 and the bottom surface of the first storage unit86) into the first chamber 86 a. The gas component that is guided to thefirst chamber 86 a is discharged to the exterior through an exhaust gasflow path 90 connected to an upper part of the first chamber 86 a in thefirst storage unit 86. A hydrogen sensor 91 in order to detect aconcentration of the hydrogen gas within the gas component is installedin the exhaust gas flow path 90. The exhaust gas flow path 90 includes anon-illustrated diffusion pipe in order to diffuse a gas component (thehydrogen gas) at a position of greater than or equal to 5 m from theground.

The amount of water in the first storage unit 86 is controlled in amanner so that a portion of the partition wall 88 is always immersed inthe water. Therefore, the first storage unit 86 also functions as awater sealing device for preventing back firing. More specifically, thefirst storage unit 86 prevents propagation of flames from the exhaustgas flow path 90 into the second chamber 86 b, for example, in the casethat the exhaust gas flow path 90 is struck by lightning. Further, thefirst storage unit 86 prevents propagation of flames from the firstoutlet port member 56 b into the exhaust gas flow path 90, for example,in the case that the first outlet port member 56 b of the cell member 12is ignited or set on fire.

The partition wall 88 also functions as a wave dissipating plate thatsuppresses waves on the water surface of the second chamber 86 b frombeing transmitted to the water surface of the first chamber 86 a at thetime of gas-liquid separation. Consequently, the water level in thefirst chamber 86 a can be stabilized. A first water level sensor LS1(first water level acquisition unit) for acquiring the amount of waterin the first storage unit 86 is installed in the first chamber 86 a ofthe first storage unit 86.

One end of the water introduction flow path 81 is connected to the firststorage unit 86. A strainer 92, a water pump 94, a first heat exchanger96, a water purification treatment unit 98, and a pure water supplyvalve 100 are installed in the water introduction flow path 81sequentially in this order from the first gas-liquid separator 80 towardthe first supply flow path 82.

The strainer 92 removes foreign matter (particulate suspended matter)from the water that is guided from the first storage unit 86. The waterpump 94 is an electric water pump for use in performing waterelectrolysis. The water pump 94 causes the water inside the firststorage unit 86 to flow through the water introduction flow path 81, thefirst supply flow path 82, the cell member 12 (the first fluid flow path44), and the first lead-out flow path 84, and be returned to the firststorage unit 86. The first heat exchanger 96 adjusts to a desiredtemperature the water that is transferred thereto from the water pump94. The first heat exchanger 96, for example, is a water-cooledintercooler.

The water purification treatment unit 98 performs a water purifyingtreatment on the water that is guided from the first heat exchanger 96.Consequently, the water, which has been separated by the firstgas-liquid separator 80 from the fluid that is led out from the cellmember 12, can be reused. Therefore, the amount of municipal water usedper unit amount of the hydrogen gas produced at the time of the waterelectrolysis mode can be reduced. Further, a replacement cycle ofcomponent parts (the activated carbon filter, the ion exchange resin,the hollow fiber filter, and the like) of the pure water production unit74 in order to convert the municipal water into pure water can belengthened. Thus, it is possible to reduce the operating cost and themaintenance cost of the water electrolysis and electricity generatingsystem 10. Furthermore, the water supplied to the cell member 12 canalways be pure water. Therefore, it is possible to reliably manage aliquid junction resistance and a ground fault resistance that arerequired for water electrolysis.

The water purification treatment unit 98 includes, for example, aplurality of ion exchangers 102 and a mesh filter 104. The plurality ofion exchangers 102 are arranged in parallel with each other.Consequently, as compared to a case in which the plurality of ionexchangers 102 are arranged in series, it is possible to reduce a lossin pressure when the water flows through the ion exchangers 102. The ionexchangers 102 preferably include, for example, replaceable cartridges.The mesh filter 104 removes foreign matter from the water that flowsthrough the ion exchangers 102. The pure water supply valve 100 is anopening/closing valve that opens and closes the first fluid flow path44.

The first supply flow path 82 introduces the water (pure water) that isguided from the water introduction flow path 81 into the first inletport member 56 a. The first lead-out flow path 84 is connected to a wallof the second chamber 86 b of the first storage unit 86.

The oxygen-containing gas device 66 includes an oxygen-containing gasflow path 106, an oxygen-containing gas introduction flow path 108, adilution flow path 110, and an oxygen-containing gas lead-out flow path112. An air filter 114, an air pump 116, an air flow meter 118(oxygen-containing gas flow rate acquisition unit), an intercooler 120,a second heat exchanger 122, and a humidifier 124 are installed in theoxygen-containing gas flow path 106 sequentially in this order from anupstream side toward a downstream side.

The air filter 114 removes foreign substances inside the air (theoxygen-containing gas). The air pump 116 supercharges (compresses) thepurified oxygen-containing gas through the air filter 114. As the airpump 116, for example, a positive displacement electric motor turbo pumpis used. Only one air pump 116 is installed in the oxygen-containing gasflow path 106.

The air flow meter 118 acquires the flow rate of the oxygen-containinggas that is guided thereto from the air pump 116. The intercooler 120cools the oxygen-containing gas, which has been raised in temperaturedue to being supercharged by the air pump 116. The intercooler 120, forexample, is an air-cooled intercooler. More specifically, theintercooler 120 adjusts the temperature of the oxygen-containing gas bycontrolling the rotational speed of a non-illustrated fan.

The second heat exchanger 122 adjusts to a desired temperature theoxygen-containing gas that is cooled by the intercooler 120. The secondheat exchanger 122, for example, is a water-cooled intercooler. Thehumidifier 124 humidifies the oxygen-containing gas that is guidedthereto from the second heat exchanger 122.

A first bypass flow path 126, which detours to avoid the humidifier 124,is installed in the oxygen-containing gas flow path 106. One end (an endon an upstream side) of the first bypass flow path 126 is connected viaa flow rate control valve 128 between the humidifier 124 and the secondheat exchanger 122 in the oxygen-containing gas flow path 106. Anotherend (an end on a downstream side) of the first bypass flow path 126 isconnected more on a downstream side than the humidifier 124 in theoxygen-containing gas flow path 106.

The flow rate control valve 128 adjusts a ratio between the flow rate ofthe oxygen-containing gas that is guided to the humidifier 124 and theflow rate of the oxygen-containing gas that is guided to the firstbypass flow path 126. An electric variable three-way valve, for example,is preferably used as the flow rate control valve 128.

The oxygen-containing gas introduction flow path 108 and the dilutionflow path 110 are connected via a first flow path switching valve 130 toan end on the downstream side of the oxygen-containing gas flow path106. The first flow path switching valve 130 is capable of switchingbetween a flow through state of the oxygen-containing gas introductionflow path 108 and a flow through state of the dilution flow path 110.

In the flow through state of the oxygen-containing gas introduction flowpath 108, the first flow path switching valve 130 permits the flow ofthe oxygen-containing gas from the oxygen-containing gas flow path 106to the oxygen-containing gas introduction flow path 108, together withblocking the flow of the oxygen-containing gas from theoxygen-containing gas flow path 106 to the dilution flow path 110. Inthe flow through state of the dilution flow path 110, the first flowpath switching valve 130 permits the flow of the oxygen-containing gasfrom the oxygen-containing gas flow path 106 to the dilution flow path110, together with blocking the flow of the oxygen-containing gas fromthe oxygen-containing gas flow path 106 to the oxygen-containing gasintroduction flow path 108. A three-way valve, for example, ispreferably used as the first flow path switching valve 130.

The oxygen-containing gas introduction flow path 108 guides theoxygen-containing gas that flows through the oxygen-containing gas flowpath 106 to the first supply flow path 82. The first supply flow path 82introduces the oxygen-containing gas that is guided from theoxygen-containing gas introduction flow path 108 into the first inletport member 56 a. Stated otherwise, at the time of the waterelectrolysis mode, the first supply flow path 82 introduces the waterthat is guided from the water introduction flow path 81 into the firstinlet port member 56 a. Further, at the time of the electricitygenerating mode, the first supply flow path 82 introduces theoxygen-containing gas that is guided from the oxygen-containing gasintroduction flow path 108 into the first inlet port member 56 a. Inother words, in the water electrolysis and electricity generating system10, the first supply flow path 82 is shared in common by the waterelectrolysis mode and the electricity generating mode.

A check valve 132 is installed in the oxygen-containing gas introductionflow path 108. The check valve 132 permits the flow of theoxygen-containing gas from the first flow path switching valve 130 tothe first supply flow path 82, and blocks the flow of the fluid from thefirst supply flow path 82 to the first flow path switching valve 130.

The dilution flow path 110 guides the oxygen-containing gas (a dilutinggas) that flows through the oxygen-containing gas flow path 106 to thesecond chamber 86 b of the first storage unit 86. The check valve 134 isinstalled in the dilution flow path 110. The check valve 134 permits theflow of the oxygen-containing gas from the first flow path switchingvalve 130 to the first storage unit 86, and blocks the flow of the fluidfrom the first storage unit 86 to the first flow path switching valve130.

At the time of the electricity generating mode, the oxygen-containinggas lead-out flow path 112 guides the oxygen containing exhaust gas,which is led out to the first lead-out flow path 84 from the firstoutlet port member 56 b of the cell member 12, to the second chamber 86b of the first storage unit 86.

The oxygen-containing gas lead-out flow path 112 is connected, via asecond flow path switching valve 136, to the first lead-out flow path84. Stated otherwise, the first lead-out flow path 84 includes anupstream side lead-out flow path 84 a on an upstream side of the secondflow path switching valve 136, and a downstream side lead-out flow path84 b on a downstream side of the second flow path switching valve 136.The second flow path switching valve 136 is capable of switching betweena flow through state of the oxygen-containing gas lead-out flow path 112and a flow through state of the downstream side lead-out flow path 84 b.

In the flow through state of the oxygen-containing gas lead-out flowpath 112, the second flow path switching valve 136 permits the flow ofthe oxygen-containing gas (the oxygen containing exhaust gas) from theupstream side lead-out flow path 84 a to the oxygen-containing gaslead-out flow path 112, together with blocking the flow of the fluid(the oxygen containing exhaust gas) from the upstream side lead-out flowpath 84 a to the downstream side lead-out flow path 84 b. In the flowthrough state of the downstream side lead-out flow path 84 b, the secondflow path switching valve 136 permits the flow of the fluid (thegas-containing water) from the upstream side lead-out flow path 84 a tothe downstream side lead-out flow path 84 b, together with blocking theflow of the fluid (the gas-containing water) from the upstream sidelead-out flow path 84 a to the oxygen-containing gas lead-out flow path112. A three-way valve, for example, is preferably used as the secondflow path switching valve 136.

The humidifier 124, a first back pressure valve 138, and a check valve140 are installed sequentially in this order in the oxygen-containinggas lead-out flow path 112 from the first lead-out flow path 84 towardthe first storage unit 86. In particular, the humidifier 124 isinstalled so as to straddle over the oxygen-containing gas introductionflow path 108 and the oxygen-containing gas lead-out flow path 112. Thehumidifier 124 humidifies the oxygen-containing gas that flows throughthe oxygen-containing gas flow path 106 by the oxygen containing exhaustgas (including the generated water) that flows through theoxygen-containing gas lead-out flow path 112. The first back pressurevalve 138 regulates the flow rate of the oxygen containing exhaust gasthat flows through the oxygen-containing gas lead-out flow path 112. Adiaphragm valve, for example, is preferably used as the first backpressure valve 138. The check valve 140 permits the flow of the oxygencontaining exhaust gas from the first back pressure valve 138 to thefirst storage unit 86, and blocks the flow of the fluid from the firststorage unit 86 to the first back pressure valve 138.

The heat exchange device 68 includes a heating medium circulation flowpath 142 through which the heating medium flows. In the heat exchangedevice 68, an antifreeze solution is preferably used as the heatingmedium. A diluted liquid (a coolant) containing 50% ethylene glycol, forexample, is preferably used as the antifreeze solution, taking intoconsideration specific heat and viscosity. However, any appropriatefluid may be used as the heating medium.

A heating medium pump 144, a heating medium radiator 146, the first heatexchanger 96, and the second heat exchanger 122 are installed in theheating medium circulation flow path 142. The heating medium pump 144causes the heating medium to be circulated through the heating mediumcirculation flow path 142. The heating medium radiator 146 is positionedon a downstream side of the heating medium pump 144 in the heatingmedium circulation flow path 142. The heating medium radiator 146carries out heat exchange between the heating medium and the atmosphere.The heating medium radiator 146 adjusts the temperature of the heatingmedium by adjusting the rotational speed of a non-illustrated fan.

The first heat exchanger 96 is positioned on a more downstream side thanthe heating medium radiator 146 in the heating medium circulation flowpath 142. The first heat exchanger 96 carries out heat exchange betweenthe water that flows through the water introduction flow path 81 and theheating medium. The second heat exchanger 122 is positioned between theheating medium radiator 146 and the first heat exchanger 96 in theheating medium circulation flow path 142. In particular, the second heatexchanger 122 is positioned on a more upstream side than the first heatexchanger 96 in the heating medium circulation flow path 142. The secondheat exchanger 122 carries out heat exchange between theoxygen-containing gas that flows through the oxygen-containing gas flowpath 106 and the heating medium.

Although illustration thereof is omitted, the heat exchange device 68further includes a heating medium tank, a pressure regulating valve, andthe like for adjusting the flow rate of the heating medium inside theheating medium circulation flow path 142.

The second device 16 comprises a supply and discharge flow path 150, asecond supply flow path 154, and a hydrogen lead-out unit 156. Thesupply and discharge flow path 150 communicates with the low pressurehydrogen pipeline 402. The second supply flow path 154 guides thehydrogen gas, which is guided to the supply and discharge flow path 150from the low pressure hydrogen pipeline 402, to the second inlet portmember 58 a of the cell member 12.

A hydrogen gas supply valve 158, a check valve 160, and an ejector 162are installed in the second supply flow path 154 sequentially in thisorder from the supply and discharge flow path 150 toward the secondinlet port member 58 a. The hydrogen gas supply valve 158 is a shutoffvalve that opens and closes the second supply flow path 154. The checkvalve 160 permits the flow of the hydrogen gas from the supply anddischarge flow path 150 to the second inlet port member 58 a, and blocksthe flow of the fluid from the second inlet port member 58 a to thesupply and discharge flow path 150. A hydrogen exhaust gas circulationflow path 176 is connected to the ejector 162. At the time of theelectricity generating mode, the hydrogen exhaust gas circulation flowpath 176 returns the hydrogen exhaust gas that is led out from thesecond outlet port member 58 b of the cell member 12 to the secondsupply flow path 154. Due to the hydrogen gas that is guided from thesupply and discharge flow path 150, the ejector 162 draws in thehydrogen exhaust gas from the hydrogen exhaust gas circulation flow path176, mixes the hydrogen exhaust gas with the hydrogen gas, anddischarges the mixed hydrogen gas to the downstream side.

A second bypass flow path 166, which detours to avoid the ejector 162,is installed in the second supply flow path 154. One end (an upstreamend) of the second bypass flow path 166 is connected between the checkvalve 160 and the ejector 162 in the second supply flow path 154.Another end of the second bypass flow path 166 is connected to a moredownstream side than the ejector 162 in the second supply flow path 154.

An injector 168 is installed in the second bypass flow path 166. Inparticular, the ejector 162 and the injector 168 are arranged inparallel with each other. The injector 168 is a solenoid valve that iscapable of adjusting the flow rate of the hydrogen gas that flowsthrough the second bypass flow path 166.

The hydrogen lead-out unit 156 includes a second lead-out flow path 170,a second gas-liquid separator 172, an intermediate lead-out flow path174, a hydrogen exhaust gas circulation flow path 176, a dehumidifyingflow path 178, and a storage flow path 180. The second lead out flowpath 170 connects the second outlet port member 58 b and the secondgas-liquid separator 172 to each other. At the time of the waterelectrolysis mode, the product hydrogen gas is led out from the secondoutlet port member 58 b to the second lead-out flow path 170. At thetime of the electricity generating mode, the hydrogen exhaust gas is letout to the second lead-out flow path 170.

A purge flow path 182 in order to guide the hydrogen exhaust gas intothe second chamber 86 b of the first storage unit 86 at the time of theelectricity generating mode is connected to the second lead-out flowpath 170. A purge valve 184 and a check valve 186 are installed in thepurge flow path 182 sequentially in this order from the second lead-outflow path 170 toward the first storage unit 86. The purge valve 184 isan opening/closing valve that opens and closes the purge flow path 182.The check valve 186 permits the flow of the hydrogen exhaust gas fromthe second lead-out flow path 170 to the first storage unit 86, andblocks the flow of the fluid from the first storage unit 86 to thesecond lead-out flow path 170.

The second gas-liquid separator 172 separates into a gas and a liquidthe product hydrogen gas which is guided from the second lead-out flowpath 170 and the hydrogen exhaust gas which is guided from the secondlead-out flow path 170. The second gas-liquid separator 172 includes thesecond storage unit 188 for storing the water that has been separatedfrom the product hydrogen gas and the hydrogen exhaust gas. Inside thesecond storage unit 188, there is installed a non-illustrated swirlguide in order to generate a spiral flow in the product hydrogen gas andthe hydrogen exhaust gas that are introduced into the second storageunit 188. Consequently, separation of the product hydrogen gas and thehydrogen exhaust gas, which are introduced into the second storage unit188, into a gas and a liquid is efficiently performed.

A second water level sensor LS2 (second water level acquisition unit)for acquiring the amount of water inside the second storage unit 188 isinstalled in the second storage unit 188. A drain flow path 190 in orderto drain the water in the second storage unit 188 is connected to abottom surface of the second storage unit 188. The drain flow path 190is connected between the purge valve 184 and the check valve 186 in thepurge flow path 182. A drain valve 192 that opens and closes the drainflow path 190 is installed in the drain flow path 190.

The intermediate lead-out flow path 174 is connected to an upper part ofthe second storage unit 188. The product hydrogen gas and the hydrogenexhaust gas from which the water has been separated inside the secondstorage unit 188 are led out to the intermediate lead-out flow path 174.The hydrogen exhaust gas circulation flow path 176 and the dehumidifyingflow path 178 are connected to the intermediate lead-out flow path 174via a third flow path switching valve 194. The third flow path switchingvalve 194 is capable of switching between a flow through state of thehydrogen exhaust gas circulation flow path 176 and a flow through stateof the dehumidifying flow path 178.

In the flow through state of the hydrogen exhaust gas circulation flowpath 176, the third flow path switching valve 194 permits the flow ofthe hydrogen exhaust gas from the intermediate lead-out flow path 174 tothe hydrogen exhaust gas circulation flow path 176, together withblocking the flow of the hydrogen exhaust gas from the intermediatelead-out flow path 174 to the dehumidifying flow path 178. In the flowthrough state of the dehumidifying flow path 178, the third flow pathswitching valve 194 permits the flow of the product hydrogen gas fromthe intermediate lead-out flow path 174 to the dehumidifying flow path178, together with blocking the flow of the product hydrogen gas fromthe intermediate lead-out flow path 174 to the hydrogen exhaust gascirculation flow path 176. A three-way valve, for example, is preferablyused as the third flow path switching valve 194.

The hydrogen exhaust gas circulation flow path 176 connects the thirdflow path switching valve 194 and the ejector 162 to each other. A checkvalve 196 is installed in the hydrogen exhaust gas circulation flow path176. The check valve 196 permits the flow of the hydrogen exhaust gasfrom the third flow path switching valve 194 to the ejector 162,together with blocking the flow of the hydrogen gas from the ejector 162to the third flow path switching valve 194.

The dehumidifying flow path 178 connects the third flow path switchingvalve 194 and the storage flow path 180 to each other. A dehumidifyingand cooling unit 198, a first dehumidifying adsorption unit 200 a, asecond dehumidifying adsorption unit 200 b, and a dehumidificationswitching unit 202 are installed in the dehumidifying flow path 178.

The dehumidifying and cooling unit 198 dehumidifies by cooling theproduct hydrogen gas. The first dehumidifying adsorption unit 200 a isinstalled more downstream than the dehumidifying and cooling unit 198 inthe dehumidifying flow path 178. The second dehumidifying adsorptionunit 200 b is installed more downstream than the first dehumidifyingadsorption unit 200 a in the dehumidifying flow path 178. The firstdehumidifying adsorption unit 200 a and the second dehumidifyingadsorption unit 200 b are dehumidifying and adsorption columns includingan adsorbent such as zeolite. The first dehumidifying adsorption unit200 a and the second dehumidifying adsorption unit 200 b includenon-illustrated heaters for restoring the adsorption function of theadsorbent. More specifically, the first dehumidifying adsorption unit200 a and the second dehumidifying adsorption unit 200 b are capable ofdehumidifying the product hydrogen gas and restoring the dehumidifyingfunction thereof.

The dehumidification switching unit 202 changes the direction in whichthe product hydrogen gas flows, in a manner so that the order in whichthe product hydrogen gas flows through the first dehumidifyingadsorption unit 200 a and the second dehumidifying adsorption unit 200 bis changed. The dehumidification switching unit 202 includes a fourthflow path switching valve 204, a first switching flow path 206, a firstopening/closing valve 208, a second switching flow path 210, and asecond opening/closing valve 212.

The fourth flow path switching valve 204 is installed in thedehumidifying flow path 178 between the dehumidifying and cooling unit198 and the first dehumidifying adsorption unit 200 a. The dehumidifyingflow path 178 includes a dehumidifying upstream flow path 178 a on anupstream side of the fourth flow path switching valve 204, and adehumidifying downstream flow path 178 b on a downstream side of thefourth flow path switching valve 204. The first switching flow path 206is connected to the fourth flow path switching valve 204.

The fourth flow path switching valve 204 is capable of switching betweena flow through state of the dehumidifying downstream flow path 178 b anda flow through state of the first switching flow path 206. In the flowthrough state of the dehumidifying downstream flow path 178 b, thefourth flow path switching valve 204 permits the flow of the producthydrogen gas from the dehumidifying upstream flow path 178 a to thedehumidifying downstream flow path 178 b, together with blocking theflow of the product hydrogen gas from the dehumidifying upstream flowpath 178 a to the first switching flow path 206. In the flow throughstate of the first switching flow path 206, the fourth flow pathswitching valve 204 permits the flow of the product hydrogen gas fromthe dehumidifying upstream flow path 178 a to the first switching flowpath 206, together with blocking the flow of the product hydrogen gasfrom the dehumidifying upstream flow path 178 a to the dehumidifyingdownstream flow path 178 b. A three-way valve, for example, ispreferably used as the fourth flow path switching valve 204.

The first switching flow path 206 is connected on a more downstream sidethan the second dehumidifying adsorption unit 200 b in the dehumidifyingdownstream flow path 178 b. The first opening/closing valve 208 isinstalled in the dehumidifying downstream flow path 178 b on a moredownstream side than a connected part of the first switching flow path206. The first opening/closing valve 208 opens and closes thedehumidifying downstream flow path 178 b. One end of the secondswitching flow path 210 is connected on a more upstream side than thefirst dehumidifying adsorption unit 200 a in the dehumidifyingdownstream flow path 178 b. Another end of the second switching flowpath 210 is connected on a more downstream side than the firstopening/closing valve 208 in the dehumidifying downstream flow path 178b. The second opening/closing valve 212 opens and closes the secondswitching flow path 210.

The storage flow path 180 guides the dehumidified product hydrogen gasthat is guided from the dehumidifying flow path 178 to the supply anddischarge flow path 150. A mesh filter 214 and a second back pressurevalve 216 are installed in the storage flow path 180 sequentially inthis order from the dehumidifying flow path 178 toward the supply anddischarge flow path 150. The mesh filter 214 removes foreign matter fromthe product hydrogen gas. The second back pressure valve 216 regulatesthe flow rate of the product hydrogen gas that flows through the storageflow path 180. A diaphragm valve, for example, is preferably used as thesecond back pressure valve 216.

A vent flow path 218 is connected within the storage flow path 180 on amore upstream side than the mesh filter 214 and the second back pressurevalve 216. The vent flow path 218 discharges the product hydrogen gasthat is guided from the dehumidifying flow path 178 to the exhaust gasflow path 90. A vent valve 220 and a check valve 222 are installed inthe vent flow path 218 sequentially in this order from the storage flowpath 180 toward the exhaust gas flow path 90. The vent valve 220 servesto open and close the vent flow path 218. The check valve 222 permitsthe flow of the product hydrogen gas from the storage flow path 180 tothe exhaust gas flow path 90, together with blocking the flow of thefluid from the exhaust gas flow path 90 to the storage flow path 180.

At the time of the electricity generating mode, the cooling device 18cools the cell member 12 by circulating the coolant through the coolantflow path 48 of the cell member 12 (refer to FIG. 3 ). An ethyleneglycol aqueous solution, for example, is preferably used as the coolant.

The cooling device 18 includes a coolant supply flow path 224, a coolantlead-out flow path 226, and a coolant radiator 228. The coolant supplyflow path 224 connects the coolant radiator 228 and the coolant inletport member 60 a to each other. A coolant pump 230 is provided in thecoolant supply flow path 224. The coolant pump 230 discharges thecoolant in the coolant supply flow path 224 toward the coolant inletport member 60 a. The coolant lead-out flow path 226 connects thecoolant outlet port member 60 b and the coolant radiator 228 to eachother.

A third back pressure valve 232 that adjusts the flow rate of thecoolant that flows through the coolant lead-out flow path 226 isinstalled in the coolant lead-out flow path 226. A diaphragm valve, forexample, is preferably used as the third back pressure valve 232. Thecoolant radiator 228 carries out heat exchange between the coolant andthe atmosphere. The coolant radiator 228 adjusts the temperature of thecoolant by adjusting the rotational speed of a non-illustrated fan.

Although illustration thereof is omitted, the cooling device 18 furtherincludes a coolant tank and a pressure regulating valve and the like inorder to adjust the flow rate of the coolant inside the coolant supplyflow path 224, the coolant lead-out flow path 226, and the coolant flowpath 48.

The water electrolysis and electricity generating system 10 furthercomprises a gas meter 234 (flow rate acquisition unit) and a system ECU236. The gas meter 234 is installed in the supply and discharge flowpath 150. The gas meter 234 acquires the flow rate of the producthydrogen gas (a sales amount of the hydrogen gas) that flows from thesupply and discharge flow path 150 to the low pressure hydrogen pipeline402, and the flow rate of the hydrogen gas (a purchase amount of thehydrogen gas) that flows from the low pressure hydrogen pipeline 402 tothe supply and discharge flow path 150.

As shown in FIG. 4 , the information acquired by the gas meter 234 istransmitted to a gateway server 238. The gateway server 238 transmitstransaction information (the hydrogen gas sales amount and the hydrogengas purchase amount) to which a time stamp is affixed to a VPP server240 (virtual power plant server). The system ECU 236 is capable ofcommunicating with the VPP server 240 via the gateway server 238. TheVPP server 240 transmits a water electrolysis mode operation request, anelectricity generating mode operation request, a mode switching request,a driving stop request, and the like to the system ECU 236 via thegateway server 238.

The system ECU 236 receives the acquired information of the first waterlevel sensor LS1, the second water level sensor LS2, the impedancemeasurement unit 52, the cell voltage measurement unit 54, the hydrogensensor 91, and the air flow meter 118. Further, the system ECU 236receives the acquired information of various sensors such as a pressuresensor, a temperature sensor, a specific resistance meter, a hydrogensensor, and a flow rate meter, etc., included in the cell member 12, thefirst device 14, the second device 16, and the cooling device 18.

The system ECU 236 comprises a computation unit 242 (processing unit)and a storage unit 246. The computation unit 242 may be configured, forexample, in the form of a processing circuit which is a processor suchas a CPU (Central Processing Unit) or the like. The computation unit 242includes a valve control unit 248, a pump control unit 250, an injectorcontrol unit 252, a determination unit 254, and a counter 256. Therespective elements (the valve control unit 248, etc.) of thecomputation unit 242 can be realized by programs stored in the storageunit 246 being executed by the computation unit 242.

At least a portion of the respective elements (the valve control unit248, etc.) of the computation unit 242 may be realized by an integratedcircuit such as an ASIC (Application Specific Integrated Circuit), anFPGA (Field-Programmable Gate Array), or the like. Further, at least aportion of the respective elements (the valve control unit 248, etc.) ofthe computation unit 242 may include an electronic circuit including adiscrete device.

The storage unit 246 includes a volatile memory and a non-volatilememory. As an example of the volatile memory, there may be cited a RAM(Random Access Memory) or the like. As an example of the non-volatilememory, there may be cited a ROM (Read Only Memory) or a flash memory orthe like. At least a portion of the storage unit 246 may be incorporatedin the aforementioned processor or the integrated circuit or the like.

The valve control unit 248 controls operations of the various valves.The pump control unit 250 controls operations of the various pumps (thewater pump 94, the air pump 116, the heating medium pump 144, and thecoolant pump 230). The injector control unit 252 controls valve openingand valve closing of the injector 168. The counter 256 serves to measurethe time.

Next, a description will be given concerning a method of operating thewater electrolysis and electricity generating system 10.

First, a description will be given concerning operations of the waterelectrolysis and electricity generating system 10 in the waterelectrolysis mode. In the case that the water electrolysis modeoperation request has been made to the system ECU 236 from the VPPserver 240 via the gateway server 238, the water electrolysis andelectricity generating system 10 carries out operations in the waterelectrolysis mode.

More specifically, as shown in FIG. 5 , during operation in the waterelectrolysis mode, pure water is produced from the municipal water (stepS1). In particular, the valve control unit 248 opens the municipal watersupply valve 72. Upon doing so, as shown in FIG. 6 , the municipal waterpasses through the water supply flow path 70 and is introduced into thepure water production unit 74. In the pure water production unit 74, thepure water is produced by flowing through an activated carbon filter, anion exchange resin, and a hollow fiber filter, none of which are shown.The pure water produced in the pure water production unit 74 isintroduced into the first storage unit 86 via the pure water regulatingvalve 76. The pure water supplied into the first storage unit 86 ismixed inside the first storage unit 86 with the water that was used atthe time of water electrolysis of the cell member 12.

Further, at the time of the water electrolysis mode, the valve controlunit 248 opens and closes the pure water regulating valve 76 based onthe water level acquired by the first water level sensor LS1 in a mannerso that the water level in the first storage unit 86 is maintainedwithin a predetermined range. More specifically, in the case that thewater level acquired by the first water level sensor LS1 has fallen to alower limit level, the valve control unit 248 opens the pure waterregulating valve 76, and supplies the pure water into the first storageunit 86 from the pure water production unit 74. Subsequently, in thecase that the water level acquired by the first water level sensor LS1has risen to a reference level, the valve control unit 248 closes thepure water regulating valve 76, and stops supplying the pure water intothe first storage unit 86 from the pure water production unit 74.Furthermore, in the case that the water level acquired by the firstwater level sensor LS1 has risen to an upper limit level, the valvecontrol unit 248 opens a drain valve installed in a non-illustrateddrain flow path connected to the bottom surface of the first storageunit 86, and discharges the water inside the first storage unit 86 tothe exterior.

Moreover, the system ECU 236 carries out a failure stopping process inthe case that the water level acquired by the first water level sensorLS1 has risen to an abnormal water level upper limit level. Further, thesystem ECU 236 carries out the failure stopping process in the case thatthe water level acquired by the first water level sensor LS1 has fallento an abnormal water level lower limit level. The lower limit level, thereference level, the upper limit level, the abnormal upper limit level,and the abnormal lower limit level of the water level inside the firststorage unit 86 are stored beforehand in the storage unit 246.

Subsequently, the valve control unit 248 controls the various valves toplace them in the water electrolysis mode state (step S2 of FIG. 5 ).More specifically, the valve control unit 248 opens the pure watersupply valve 100, the first opening/closing valve 208, and the secondback pressure valve 216. Further, the valve control unit 248 closes thehydrogen gas supply valve 158, the purge valve 184, the drain valve 192,the second opening/closing valve 212, and the vent valve 220. Moreover,the first back pressure valve 138 and the third back pressure valve 232may be either open or closed.

Further, the valve control unit 248 controls the flow rate control valve128 to bring about a state in which, together with the oxygen-containinggas flowing through the first bypass flow path 126, theoxygen-containing gas does not flow through the humidifier 124.Furthermore, the valve control unit 248 controls the first flow pathswitching valve 130 to bring about the flow through state of thedilution flow path 110. The valve control unit 248 controls the secondflow path switching valve 136 to bring about the flow through state ofthe downstream side lead-out flow path 84 b. The valve control unit 248controls the third flow path switching valve 194 to bring about the flowthrough state of the dehumidifying flow path 178. The valve control unit248 controls the fourth flow path switching valve 204 to bring about theflow through state of the dehumidifying downstream flow path 178 b.

Next, the pump control unit 250 controls the various pumps to place themin the water electrolysis mode state (step S3 of FIG. 5 ). Morespecifically, the pump control unit 250 drives the water pump 94, theheating medium pump 144, and the air pump 116. Moreover, the pumpcontrol unit 250 does not drive the coolant pump 230. However, in thecase that the exterior air is in a high temperature environment (forexample, 45° C. or higher), the pump control unit 250 may drive thecoolant pump 230 and thereby cool the cell member 12.

Upon doing so, the water that is stored in the first storage unit 86passes through the water introduction flow path 81, and is superchargedby the water pump 94 after the foreign matter has been removed therefromby the strainer 92. The water that is supercharged by the water pump 94is adjusted to a desired temperature by carrying out heat exchange withthe heating medium in the first heat exchanger 96.

Concerning the water that has flowed through the first heat exchanger96, after passing through the ion exchangers 102 and being subjected toa water purifying treatment, foreign matter is removed therefrom by themesh filter 104. Next, the water (pure water) that has flowed throughthe mesh filter 104 is supplied to the first inlet port member 56 a ofthe cell member 12 via the first supply flow path 82 (step S4 of FIG. 5). Moreover, the system ECU 236 carries out the failure stopping processin the case that the specific resistance of the water (pure water), asmeasured at a position on a downstream side of the mesh filter 104 inthe water introduction flow path 81, has fallen below a lower limitlevel.

The pure water that is introduced into the first inlet port member 56 aflows through the first fluid flow path 44 of the cell member 12 and isguided to the first electrode 30. When operating in the waterelectrolysis mode, since the hydrogen gas supply valve 158 is closed,the hydrogen gas is not introduced into the second inlet port member 58a of the cell member 12.

Further, the oxygen-containing gas that has flowed into theoxygen-containing gas flow path 106 is supercharged by the air pump 116after the foreign matter has been removed therefrom by the air filter114. The oxygen-containing gas which has been raised in temperature dueto supercharging flows through the air flow meter 118, and after havingbeen cooled by the intercooler 120, is adjusted to a desired temperatureby the second heat exchanger 122.

The oxygen-containing gas that has flowed through the second heatexchanger 122 passes through the first bypass flow path 126 and isguided to the dilution flow path 110. In particular, in the waterelectrolysis mode, the oxygen-containing gas does not flow through thehumidifier 124. Therefore, at the time of the water electrolysis mode,it is possible to prevent the humidifier 124 from becoming dried up bythe oxygen-containing gas. Consequently, at a time when switching fromoperating in the water electrolysis mode to operating in the electricitygenerating mode, and immediately after the generation of electricity hasbeen started, the amount by which the oxygen-containing gas ishumidified can be efficiently adjusted by the humidifier 124. Theoxygen-containing gas that is guided to the dilution flow path 110 isintroduced into the second chamber 86 b of the first storage unit 86.

Thereafter, the system ECU 236 initiates water electrolysis (step S5 ofFIG. 5 ). In particular, the system ECU 236 drives the electrolyticpower source 50 and applies a voltage to the cell member 12. Upon doingso, at the first electrode 30 of each of the cells 20, pure water iselectrolyzed to thereby generate hydrogen ions, electrons, and oxygengas. At the second electrode 32 of each of the cells 20, the hydrogenions, which have permeated through the electrolyte membrane 28 from thefirst electrode 30, and electrons, which have been guided from the firstelectrode 30 to the second electrode 32, are combined to producehydrogen gas. At this time, a portion of the product hydrogen gasproduced at the second electrodes 32 permeates through the electrolytemembranes 28 and is guided to the first fluid flow path 44.

Therefore, gas-containing water, in which there are included oxygen gasgenerated due to the reaction, unreacted water that has not beensubjected to electrolysis, and generated hydrogen that has permeatedfrom the second electrodes 32 to the first electrodes 30 via theelectrolyte membranes 28, is introduced into the first outlet portmember 56 b. Further, the product hydrogen gas is guided to the secondoutlet port member 58 b. Moreover, the product hydrogen gas is alsoguided to the second inlet port member 58 a. However, since the checkvalve 160 is installed in the second supply flow path 154, the producthydrogen gas that is guided to the second inlet port member 58 a doesnot flow into the supply and discharge flow path 150. Further, since thecheck valve 196 is installed in the hydrogen exhaust gas circulationflow path 176, the product hydrogen gas that is guided to the secondinlet port member 58 a does not flow into the third flow path switchingvalve 194.

The gas-containing water that is guided to the first outlet port member56 b of the cell member 12 flows into the first gas-liquid separator 80via the first lead-out flow path 84. More specifically, thegas-containing water flows into the second chamber 86 b of the firststorage unit 86. Further, the oxygen-containing gas is introduced fromthe dilution flow path 110 into the second chamber 86 b of the firststorage unit 86. Therefore, the oxygen-containing gas in the secondchamber 86 b passes within the water that is stored in the first storageunit 86 (via a route between the partition wall 88 and the bottomsurface of the first storage unit 86) and flows into the first chamber86 a. At this time, the gas component contained within thegas-containing water is also guided to the first chamber 86 a. Statedotherwise, the gas component that is separated from the gas-containingwater flows into the first chamber 86 a, and the water (liquid water)that is separated from the gas-containing water is stored in the firststorage unit 86. Next, the gas component that has flowed into the firstchamber 86 a, in a state of being diluted by the oxygen-containing gas,is exhausted to the exterior through the exhaust gas flow path 90.

The product hydrogen gas that is guided to the second outlet port member58 b of the cell member 12 flows into the second gas-liquid separator172 via the second lead-out flow path 170. At this time, since the purgevalve 184 is closed, the product hydrogen gas that flows through thesecond lead-out flow path 170 is not guided to the first gas-liquidseparator 80 via the purge flow path 182.

The product hydrogen gas that is guided to the second gas-liquidseparator 172 flows in a spiral shape inside the second storage unit188, and is separated into a gas and a liquid. The water (liquid water)that has been separated from the product hydrogen gas is stored in thesecond storage unit 188. The product hydrogen gas from which the waterhas been separated is guided to the intermediate lead-out flow path 174.

The product hydrogen gas that is guided to the intermediate lead-outflow path 174 flows into the dehumidifying flow path 178 via the thirdflow path switching valve 194 and is dehumidified. More specifically,the product hydrogen gas, which has flowed into the dehumidifyingupstream flow path 178 a from the third flow path switching valve 194,is cooled and dehumidified by the dehumidifying and cooling unit 198.Thereafter, the product hydrogen gas is guided from the dehumidifyingupstream flow path 178 a to the dehumidifying downstream flow path 178 bvia the fourth flow path switching valve 204. The product hydrogen gas,which is guided to the dehumidifying downstream flow path 178 b, flowssequentially in this order through the first dehumidifying adsorptionunit 200 a and the second dehumidifying adsorption unit 200 b, and thenflows into the storage flow path 180. At this time, the product hydrogengas is adsorbed and dehumidified by the first dehumidifying adsorptionunit 200 a and the second dehumidifying adsorption unit 200 b. In thiscase, for example, the residual water content of the product hydrogengas can be controlled to be less than a predetermined value, by carryingout a restorative process (self-regeneration) to restore the adsorptionfunction of the first dehumidifying adsorption unit 200 a and the seconddehumidifying adsorption unit 200 b.

The product hydrogen gas that has flowed into the storage flow path 180,after the foreign matter has been removed therefrom by the mesh filter214, is led out to the low pressure hydrogen pipeline 402 via the secondback pressure valve 216 and the supply and discharge flow path 150.Moreover, the valve control unit 248 feedback controls the second backpressure valve 216 in a manner so that the pressure of the producthydrogen gas at a position in the vicinity of the upstream side of thesecond back pressure valve 216 in the storage flow path 180 becomesgreater than or equal to a predetermined transport pressure.

At this time, the gas meter 234 acquires the flow rate of the producthydrogen gas (the sales amount of the product hydrogen gas) that flowsfrom the supply and discharge flow path 150 into the low pressurehydrogen pipeline 402, and transmits the acquired amount to the VPPserver 240 via the gateway server 238. Consequently, the series ofoperation flows that describe the water electrolysis mode of the waterelectrolysis and electricity generating system 10 are brought to an end.

During operation in the above-described water electrolysis mode, theheating medium (the antifreeze) that flows through the first heatexchanger 96 carries out heat exchange directly with the exterior air bythe heating medium radiator 146. Stated otherwise, in the first heatexchanger 96, the water transferred by the water pump 94 does not carryout heat exchange directly with the exterior air. Therefore, even if theexterior air is below the freezing point, it is possible to prevent thewater in the first supply flow path 82 from freezing. Further, accordingto the present embodiment, the water circulation unit 64 is installedtogether with the cell member 12 in a non-illustrated housing having anexplosion-proof ventilation and heat-retaining function. Consequently,even if the temperature of the exterior air is below the freezing point,it is possible to prevent freezing of the water by supercooling andenhance the temperature control characteristics.

The pump control unit 250 feedback controls the rotational speed (thecirculating flow rate of the heating medium) of the heating medium pump144 in a manner so that the temperature of the gas-containing water thatis led out from the first outlet port member 56 b of the cell member 12lies within a predetermined temperature range. Consequently, even if thecell member 12 rises to an excessive voltage and the amount of heatincreases accompanying deterioration over time, the temperature of thecell member 12 can be kept within an upper limit of the operatingtemperature. Moreover, in the case that the temperature of the heatingmedium temperature at the outlet of the heating medium radiator 146falls below a preset lower limit temperature (for example, −25° C.), thesystem ECU 236 carries out the failure stopping process withoutactivating the heating medium pump 144. Further, similarly, the systemECU 236 also performs the failure stopping process in the case that thewater temperature at the outlet of the first heat exchanger 96 hasbecome lower than a predicted freezing temperature (for example, 1° C.).This is because, if the exterior air temperature is too low, the watermay become frozen inside the first heat exchanger 96, even if the flowrate of the heating medium is reduced.

Further, the heating medium that flows through the second heat exchanger122 is guided to the first heat exchanger 96 on a more downstream sidethan the air pump 116, in a state of having been warmed by the exhaustheat of the oxygen-containing gas that is supercharged by the air pump116. Therefore, even in the case that the exterior air is below thefreezing point, the first heat exchanger 96 is capable of effectivelysuppressing freezing of the water that flows through the first supplyflow path 82.

The pump control unit 250 feedback controls the rotational speed of theair pump 116 in a manner so that the supplied flow rate of theoxygen-containing gas acquired by the air flow meter 118 becomes adilution flow rate. The dilution flow rate is a flow rate such that theconcentration of the hydrogen gas in the vicinity of the outlet of thefirst storage unit 86 in the exhaust gas flow path 90 does not exceed anupper limit value.

The air pump 116 functions as a dilution pump in the water electrolysismode. Further, as will be discussed later, the air pump 116 alsofunctions as a pump for supplying the oxygen gas in the electricitygenerating mode. In this case, since the air pump 116 is capable ofensuring a dilution flow rate equivalent to that at a time of maximumrated electricity generation, in the water electrolysis mode, theconcentration of the hydrogen gas that is discharged from the firstgas-liquid separator 80 can be reliably controlled to be less than anupper limit value. Moreover, the system ECU 236 stops operation of thewater electrolysis mode in the case that the concentration of hydrogengas discharged from the first gas-liquid separator 80 becomes greaterthan or equal to the upper limit value.

In the case that the water level acquired by the second water levelsensor LS2 has risen to an upper limit level, the valve control unit 248opens the drain valve 192, and discharges the water inside the secondstorage unit 188 into the second chamber 86 b of the first storage unit86. Next, in the case that the water level acquired by the second waterlevel sensor LS2 has fallen to the lower limit level, the valve controlunit 248 closes the drain valve 192 and terminates the water drainageprocess of the second storage unit 188.

Further, the system ECU 236 carries out a failure stopping process inthe case that the water level acquired by the second water level sensorLS2 has risen to an abnormal water level upper limit level. Furthermore,the system ECU 236 carries out the failure stopping process in the casethat the water level acquired by the second water level sensor LS2 hasfallen to an abnormal water level lower limit level. Even in the casethat a portion of the product hydrogen gas inside the second storageunit 188 blows into the second chamber 86 b of the first storage unit86, the product hydrogen gas that has flowed into the first storage unit86 is released to the atmosphere in a fully diluted state due to theoxygen-containing gas. The lower limit level, the upper limit level, theabnormal upper limit level, and the abnormal lower limit level of thewater level inside the second storage unit 188 are stored beforehand inthe storage unit 246.

According to the present embodiment, the flow of the product hydrogengas is switched in a manner so that the order in which the producthydrogen gas flows through the first dehumidifying adsorption unit 200 aand the second dehumidifying adsorption unit 200 b is changed. Morespecifically, as shown in FIG. 7 , during operation of the waterelectrolysis mode, the valve control unit 248 controls the fourth flowpath switching valve 204 to bring about the flow through state of thefirst switching flow path 206, and together with closing the firstopening/closing valve 208, opens the second opening/closing valve 212.Upon doing so, the product hydrogen gas, which is guided from thedehumidifying upstream flow path 178 a to the fourth flow path switchingvalve 204, is guided to the first switching flow path 206. The producthydrogen gas, which is guided to the first switching flow path 206,flows sequentially in this order through the second dehumidifyingadsorption unit 200 b and the first dehumidifying adsorption unit 200 a,and then flows into the storage flow path 180 via the second switchingflow path 210. At this time, the product hydrogen gas is adsorbed anddehumidified by the second dehumidifying adsorption unit 200 b and thefirst dehumidifying adsorption unit 200 a. In this manner, by changingthe order in which the product hydrogen gas flows through the firstdehumidifying adsorption unit 200 a and the second dehumidifyingadsorption unit 200 b, the replacement interval of the dehumidifyingadsorption units can be prolonged.

Next, a description will be given concerning the electricity generatingmode of the water electrolysis and electricity generating system 10. Inthe case that the electricity generating mode operation request has beenmade to the system ECU 236 from the VPP server 240 via the gatewayserver 238, the water electrolysis and electricity generating system 10carries out operations in the electricity generating mode.

More specifically, as shown in FIG. 8 , the valve control unit 248controls the various valves in the electricity generating mode state(step S6). In particular, as shown in FIG. 9 , the valve control unit248 opens the first back pressure valve 138, the hydrogen gas supplyvalve 158, the purge valve 184, the drain valve 192, and the third backpressure valve 232. The valve control unit 248 closes the pure watersupply valve 100 and the second back pressure valve 216. Moreover, thefirst opening/closing valve 208, the second opening/closing valve 212,and the vent valve 220 may be either open or closed.

Further, by the valve control unit 248 controlling the flow rate controlvalve 128, the oxygen-containing gas is made to flow to the humidifier124 and the first bypass flow path 126. Furthermore, the valve controlunit 248 controls the first flow path switching valve 130 to bring aboutthe flow through state of the oxygen-containing gas introduction flowpath 108. The valve control unit 248 controls the second flow pathswitching valve 136 to bring about the flow through state of theoxygen-containing gas lead-out flow path 112. The valve control unit 248controls the third flow path switching valve 194 to bring about the flowthrough state of the hydrogen exhaust gas circulation flow path 176. Itis immaterial which flow through state the fourth flow path switchingvalve 204 is placed in.

Next, the pump control unit 250 controls the various pumps to place themin the electricity generating mode state (step S7 of FIG. 8 ). Morespecifically, the pump control unit 250 drives the air pump 116, theheating medium pump 144, and the coolant pump 230. Moreover, the pumpcontrol unit 250 does not drive the water pump 94. Further, inaccordance with preset load conditions, the injector control unit 252drives the injector 168 to be opened and closed in a valve opening timeperiod and a valve closing time period.

Upon doing so, the oxygen-containing gas that has flowed into theoxygen-containing gas flow path 106 is supercharged by the air pump 116on a more downstream side than the air pump 116 after the foreign matterhas been removed therefrom by the air filter 114. The oxygen-containinggas which has been raised in temperature due to supercharging flowsthrough the air flow meter 118, and after having been cooled by theintercooler 120, is adjusted to a desired temperature by the second heatexchanger 122.

The oxygen-containing gas that has flowed through the second heatexchanger 122 is made to flow separately through the humidifier 124 andthe first bypass flow path 126 by the flow rate control valve 128, andthe flows thereof are combined on a more downstream side than thehumidifier 124 in the oxygen-containing gas flow path 106. Thereafter,the oxygen-containing gas is introduced into the first inlet port member56 a of the cell member 12 via the first flow path switching valve 130,the oxygen-containing gas introduction flow path 108, and the firstsupply flow path 82 (step S8 of FIG. 8 ).

Further, the hydrogen gas supplied from the hydrogen station 400 to thesupply and discharge flow path 150 via the low pressure hydrogenpipeline 402 is introduced into the hydrogen gas supply valve 158 andthe second supply flow path 154. Next, the check valve 160 is openedafter the pressure inside the second supply flow path 154 has been helduntil becoming equivalent to the transport pressure in the low pressurehydrogen pipeline 402. At this time, the gas meter 234 acquires the flowrate (the purchase amount of the hydrogen gas) of the hydrogen gassupplied from the low pressure hydrogen pipeline 402 to the supply anddischarge flow path 150, and transmits the acquired amount to the VPPserver 240 via the gateway server 238.

The hydrogen gas that is guided to a more downstream side of the secondsupply flow path 154 than the check valve 160 is guided to the ejector162 and the injector 168. The hydrogen gas that is discharged from theinjector 168 and the hydrogen gas that is led out from the ejector 162are mixed with each other and introduced into the second inlet portmember 58 a (step S9 in FIG. 8 ).

In the cell member 12, the oxygen-containing gas that is introduced intothe first inlet port member 56 a is supplied to the first fluid flowpath 44. The hydrogen gas that is introduced into the second inlet portmember 58 a is supplied to the second fluid flow path 46. Thereafter, ineach of the MEAs 22, the oxygen-containing gas supplied to the firstelectrode 30 and the hydrogen gas supplied to the second electrode 32are consumed by undergoing electrochemical reactions in the firstelectrode catalyst layer 34 and the second electrode catalyst layer 38.As a result, generation of electricity is initiated (step S10 of FIG. 8). At this time, generated water is generated at the first electrode 30.Further, a portion of the generated water spreads from the firstelectrode 30 to the second electrode 32 via the MEA 22.

The oxygen containing exhaust gas (in which the generated water isincluded) in the first electrode 30 is led out to the first outlet portmember 56 b. The oxygen containing exhaust gas that is led out to thefirst outlet port member 56 b is guided to the oxygen-containing gaslead-out flow path 112 via the upstream side lead-out flow path 84 a andthe second flow path switching valve 136. The oxygen containing exhaustgas that is guided to the oxygen-containing gas lead-out flow path 112humidifies the oxygen-containing gas that flows through theoxygen-containing gas flow path 106 at the time of flowing through thehumidifier 124. Thereafter, the oxygen containing exhaust gas flowsthrough the first back pressure valve 138 and flows into the secondchamber 86 b of the first storage unit 86.

The hydrogen exhaust gas (including unreacted hydrogen gas and generatedwater) at the second electrode 32 is led out to the second outlet portmember 58 b. The hydrogen exhaust gas that is led out to the secondoutlet port member 58 b flows through the second lead-out flow path 170and is guided to the purge flow path 182 and the second gas-liquidseparator 172. The hydrogen exhaust gas that is guided to the purge flowpath 182 passes through the check valve 186 and flows into the secondchamber 86 b of the first storage unit 86. The hydrogen exhaust gas thathas flowed into the second chamber 86 b is diluted by the oxygencontaining exhaust gas that has flowed into the second chamber 86 b fromthe oxygen-containing gas lead-out flow path 112, together with beingguided to the first chamber 86 a via the route (within the water)between the partition wall 88 and the bottom surface of the firststorage unit 86. Thereafter, the diluted oxygen containing exhaust gasis discharged to the exterior from the exhaust gas flow path 90.Consequently, the concentration of the hydrogen gas discharged from thewater electrolysis and electricity generating system 10 when operatingin the electricity generating mode can be controlled to be less than orequal to a predetermined value.

The hydrogen exhaust gas that has flowed into the second storage unit188 of the second gas-liquid separator 172, by flowing in a spiralshape, is separated into a gas and a liquid. The hydrogen exhaust gasfrom which the water has been separated inside the second storage unit188 is drawn into the ejector 162 via the intermediate lead-out flowpath 174, the third flow path switching valve 194, and the hydrogenexhaust gas circulation flow path 176, whereby the hydrogen exhaust gasis reused in the cell member 12 for generating electricity.Consequently, self-humidification of the hydrogen gas is performed bythe generated water within the hydrogen exhaust gas. Further, duringoperation in the electricity generating mode, the amount of hydrogen gasthat is used can be reduced with respect to a unit amount of generatedelectricity of the cell member 12.

The coolant that is transferred by the coolant pump 230 is introducedfrom the coolant supply flow path 224 into the coolant inlet port member60 a of the cell member 12. The coolant that is introduced into thecoolant inlet port member 60 a flows through the coolant flow path 48 tocool the cell member 12, and then is led out to the coolant outlet portmember 60 b. The coolant that is led out to the coolant outlet portmember 60 b is guided to the coolant radiator 228 via the coolantlead-out flow path 226, carries out heat exchange with (is cooled by)the atmosphere, and then is returned to the coolant supply flow path224. Consequently, the series of operation flows that describe theelectricity generating mode of the water electrolysis and electricitygenerating system 10 are brought to an end.

During operation in the above-described electricity generating mode, thesystem ECU 236 feedback controls the rotational speed of anon-illustrated fan of the intercooler 120 in a manner so that thetemperature of the oxygen-containing gas at the outlet of theintercooler 120 lies within a predetermined temperature range. Further,the heating medium (the antifreeze) that flows through the second heatexchanger 122 carries out heat exchange directly with the exterior airby the heating medium radiator 146. Stated otherwise, in the second heatexchanger 122, the oxygen-containing gas that is supercharged by the airpump 116 does not directly carry out heat exchange with the exteriorair. Therefore, even if the exterior air is below the freezing point, byreducing the flow rate of the heating medium that flows through theheating medium circulation flow path 142, it is possible to preventexcessive cooling of the oxygen-containing gas and to improve thetemperature control characteristics. Further, the pump control unit 250feedback controls the rotational speed (the circulation flow rate of theheating medium) of the heating medium pump 144 in a manner so that thetemperature of the oxygen-containing gas that is led out from the outletof the second heat exchanger 122 lies within a predetermined range.

Further, the system ECU 236 calculates a contained water amount insidethe cell member 12 from the hydrogen concentration acquired by thehydrogen sensor 91, an output requirement value of the cell member 12,and a DC resistance value of the cell member 12 acquired by theimpedance measurement unit 52. Next, the pump control unit 250 feedbackcontrols the rotational speed of the air pump 116 in a manner so thatthe contained water amount inside the cell member 12 becomes within apredetermined range, and further, the flow rate of the oxygen-containinggas acquired by the air flow meter 118 becomes a flow rate that isgreater than or equal to a set stoichiometric value of a target load.

Furthermore, the valve control unit 248 controls the degree of openingof the flow rate control valve 128 (a flow rate ratio between theoxygen-containing gas flowing through the humidifier 124 and theoxygen-containing gas flowing through the first bypass flow path 126) ina manner so that drying up (a rise in resistance due to drying of theelectrolyte membranes 28) of the cell member 12 does not occur.

Further, the valve control unit 248 feedback controls the first backpressure valve 138 in a manner so that, in the first supply flow path82, the pressure of the oxygen-containing gas in the vicinity of thefirst inlet port member 56 a of the cell member 12 lies within apredetermined range.

Furthermore, by the injector control unit 252 controlling the valveopening time period and the valve closing time period (a valve openinginterval) of the injector 168 based on the target load of the cellmember 12, the pressure of the hydrogen gas, and the temperature of thehydrogen gas, a desired stoichiometric setting value is brought about.The pressure of the hydrogen gas is a pressure of the hydrogen gas inthe vicinity of the second inlet port member 58 a in the second supplyflow path 154. The temperature of the hydrogen gas is a temperature ofthe hydrogen gas in the vicinity of the second inlet port member 58 a inthe second supply flow path 154. The injector 168 introduces thehydrogen gas into the second inlet port member 58 a of the cell member12 as a pulse flow. Therefore, a differential pressure required fordrainage inside the second fluid flow path 46 of the cell member 12 canbe secured with a smaller amount of gas, compared to a steady flow.However, a pump in order to cause the hydrogen exhaust gas to circulatemay be installed in the hydrogen exhaust gas circulation flow path 176,and the drainage of the second fluid flow path 46 may be assisted bysuch a pump.

Further, in the case that the water level acquired by the second waterlevel sensor LS2 has risen to an upper limit level, the valve controlunit 248 opens the drain valve 192, and discharges the water inside thesecond storage unit 188 into the second chamber 86 b of the firststorage unit 86. Next, in the case that the water level acquired by thesecond water level sensor LS2 has fallen to the lower limit level, thevalve control unit 248 closes the drain valve 192 and terminates thewater drainage process of the second storage unit 188. Further, thesystem ECU 236 carries out a failure stopping process in the case thatthe water level acquired by the second water level sensor LS2 has risento an abnormal water level upper limit level. Furthermore, the systemECU 236 carries out the failure stopping process in the case that thewater level acquired by the second water level sensor LS2 has fallen toan abnormal water level lower limit level.

During operation in the electricity generating mode, in the case that adeviation in the specified cell voltage variation of the cell member 12has exceeded a threshold value, there is a possibility that the interiorof the second fluid flow path 46 may become blocked by residual water.Further, in this case, there is a possibility that the hydrogen at thesecond electrode 32 may become insufficient due to nitrogen gas derivedfrom the air that has passed through the electrolyte membrane 28 fromthe first fluid flow path 44. It should be noted that the deviation inthe cell voltage variation is defined by a difference when a lowest cellvoltage is subtracted from an average cell voltage of all of the cells20. In this case, the valve control unit 248 intermittently opens thepurge valve 184 to carry out purging of the second fluid flow path 46.Consequently, stable generation of electricity can be performed. At thistime, the injector control unit 252 and the valve control unit 248feedback control the valve opening time period and the valve closingtime period (the valve opening interval) of the injector 168 and thepurge valve 184 in a manner so that the pressure of the hydrogen gas inthe vicinity of the second inlet port member 58 a of the second supplyflow path 154 is satisfied to lie within a fluctuating allowabledeviation width of the operating pressure of the second inlet portmember 58 a under the preset load conditions.

Next, a description will be given concerning a process of switching fromthe water electrolysis mode to the electricity generating mode in themethod of operating the water electrolysis and electricity generatingsystem 10.

As shown in FIG. 10 , when a request is made from the VPP server 240 tothe system ECU 236 via the gateway server 238 to switch from the waterelectrolysis mode to the electricity generating mode, a waterelectrolysis stopping step is performed (step S11). In the waterelectrolysis stopping step, the system ECU 236 stops applying thevoltage to the cell member 12 by the electrolytic power source 50.

Thereafter, a purging step of removing the residual water in the firstfluid flow path 44 of the cell member 12 and the first supply flow path82 is performed (step S12).

More specifically, in the purging step, the valve control unit 248controls the various valves to place them in a first switching mode(step S13 of FIG. 11 ). In greater detail, as shown in FIG. 12 , thevalve control unit 248 closes the pure water supply valve 100 and thehydrogen gas supply valve 158, fully opens the first back pressure valve138, and fully closes the second back pressure valve 216. Further, thevalve control unit 248 controls the flow rate control valve 128 to bringabout a state in which, while flowing through the first bypass flow path126, the oxygen-containing gas does not flow through the humidifier 124.Furthermore, the valve control unit 248 controls the first flow pathswitching valve 130 to bring about the flow through state of theoxygen-containing gas introduction flow path 108. Further, the valvecontrol unit 248 controls the second flow path switching valve 136 tobring about the flow through state of the oxygen-containing gas lead-outflow path 112.

Next, the pump control unit 250 controls the various pumps to place themin the first switching mode (step S14 of FIG. 11 ). In particular, thepump control unit 250 drives the air pump 116 at a maximum rated flowrate. Moreover, the pump control unit 250 does not initiate driving ofthe water pump 94 and the coolant pump 230.

Upon doing so, the oxygen-containing gas that has flowed into theoxygen-containing gas flow path 106 is supercharged by the air pump 116after the foreign matter has been removed therefrom by the air filter114. The oxygen-containing gas which has been raised in temperature dueto supercharging flows through the air flow meter 118, and after havingbeen cooled by the intercooler 120, is adjusted to a desired temperatureby the second heat exchanger 122.

The oxygen-containing gas that has flowed through the second heatexchanger 122 flows from the flow rate control valve 128 and through thefirst bypass flow path 126 to detour around the humidifier 124.Thereafter, the oxygen-containing gas is introduced into the first inletport member 56 a of the cell member 12 via the first flow path switchingvalve 130, the oxygen-containing gas introduction flow path 108, and thefirst supply flow path 82. At this time, the water (residual water)remaining in a portion of the oxygen-containing gas introduction flowpath 108 and a portion of the first supply flow path 82 can be washedaway toward the first inlet port member 56 a.

The oxygen-containing gas that was introduced into the first inlet portmember 56 a flows into the first outlet port member 56 b while washingaway the residual water that remains in the first fluid flow path 44. Atthis time, the oxygen-containing gas dries the first gas diffusion layer36 (see FIG. 3 ) that was submerged at the time of the waterelectrolysis mode. Consequently, the volatility of the first gasdiffusion layer 36 can be restored. The oxygen-containing gas, in whichthere is included the residual water that is led out from the firstoutlet port member 56 b to the upstream side lead-out flow path 84 a, isguided to the first storage unit 86 via the second flow path switchingvalve 136 and the oxygen-containing gas flow path 106.

Further, as shown in FIG. 11 , when the air pump 116 is started at amaximum rated level of operation, the system ECU 236 starts the counter256 (step S15). Next, the determination unit 254 determines whether ornot the flow rate of the oxygen-containing gas (a measured value of theoxygen-containing gas flow rate) acquired by the air flow meter 118 hasreached a desired rated flow rate range (step S16). In the case that themeasured value of the oxygen-containing gas flow rate does not reach thedesired rated flow rate range (step S16: NO), the pump control unit 250increases the rotational speed of the air pump 116 (step S17).Thereafter, the process of step S16 is performed again.

In the case that the measured value of the oxygen-containing gas flowrate has reached the desired rated flow rate range (step S17: YES), thedetermination unit 254 determines whether or not a measured time periodt of the counter 256 has reached a predetermined time period t1 (stepS18). In the case that the measured time period t of the counter 256 hasnot reached the predetermined time period t1, the process of step S18 isrepeated. The predetermined time period t1 is preferably set, forexample, to a time period on the order of ten seconds.

If the measured time period t of the counter 256 reaches thepredetermined time period t1 (step S18: YES), the impedance measurementunit 52 starts measuring the DC resistance component of the cell member12 (step S19). Next, the determination unit 254 determines whether ornot the DC resistance component (a measured value of the DC resistancecomponent, the contained water amount of the cell member 12) measured bythe impedance measurement unit 52 lies within a predetermined range(step S20). Stated otherwise, by using the measured value of the DCresistance component, the determination unit 254 determines whether ornot the contained water amount of the cell member 12 lies within thepredetermined range. In the case that the measured value of the DCresistance component does not lie within the predetermined range, theprocess of step S20 is repeated.

In the case that the measured value of the DC resistance component lieswithin the predetermined range (step S20: YES), the purging step isterminated, and an electricity generation preparatory step is performed(step S21).

In the electricity generation preparatory step, as shown in FIG. 13 ,the pump control unit 250 drives the air pump 116 under a low loadcondition (a load condition that is lower than a required load value atthe time of the electricity generating mode) (step S22). Statedotherwise, the pump control unit 250 reduces the rotational speed of theair pump 116.

Subsequently, the valve control unit 248 controls the flow rate controlvalve 128 to bring about a state in which the oxygen-containing gasflows through the humidifier 124 and the first bypass flow path 126.Consequently, the oxygen-containing gas that has passed through thehumidifier 124 is guided to the cell member 12 (step S23). Further, thevalve control unit 248 opens the hydrogen gas supply valve 158 (stepS24). Consequently, the hydrogen gas, which has flowed from the lowpressure hydrogen pipeline 402 into the supply and discharge flow path150, is guided to the cell member 12. Further, the injector control unit252 drives the injector 168 under a low load condition (step S25).Consequently, each of the cells 20 of the cell member 12 generateselectricity under the low load condition.

Thereafter, the determination unit 254 determines whether or not anelectricity generation starting condition has been satisfied (step S26).More specifically, the determination unit 254 determines whether or notthe cell voltage (cell voltage measurement value) of each of the cells20 measured by the cell voltage measurement unit 54 reaches a value ofgreater than or equal to a predetermined value, and a deviation in thecell voltage variation lies within a predetermined deviation. In thecase that the measured cell voltage reaches a value of greater than orequal to the predetermined value, and the deviation in the cell voltagevariation does not lie within the predetermined deviation (step S26:NO), the process of step S26 is repeated.

In the case that the measured cell voltage reaches a value of greaterthan or equal to the predetermined value, and the deviation in the cellvoltage variation lies within the predetermined deviation (step S26:YES), the system ECU 236 implements an electricity generation startingstep of causing the cell member 12 to generate electricity based on apredetermined required load value (step S27 in FIG. 10 ). At this time,the system ECU 236 slope-controls (increases at a constant rate)application of a load current to the cell member 12 in a manner so as tosatisfy a predetermined electricity generating condition. Further, basedon a required load value needed to supplement the system electricalpower, the system ECU 236 determines the amount of hydrogen gas suppliedto the cell member 12 and the load current.

In the purging step, at a time of switching from the water electrolysismode to the electricity generating mode, measurement of the impedance isset between 1 kHz and 10 kHz. Further, in the purging step, asuperimposed current of an AC impedance sine wave is on the order of ±2A. Since the contained water amount of the cell member 12 can becontrolled to reside within a predetermined range, drying up (a rise inresistance due to drying of the electrolyte membrane 28) can be reliablyprevented. In particular, when the electrolyte membrane 28 experienceslocalized drying in the vicinity of the first inlet port member 56 a, areaction distribution in the surfaces of the cell electrodes isgenerated when the generation of electricity is started, and thegeneration of electricity tends to become unstable. When this occurs,there is a possibility that generation of heat at the dried portion mayaccelerate the deterioration of the electrolyte membrane 28. However, bycontrolling the contained water amount of the cell member 12,deterioration of the electrolyte membrane 28 due to localized drying ofthe electrolyte membrane 28 can be prevented. Consequently, it ispossible to stabilize the generation of electricity.

Next, a description will be given concerning a process of switching fromthe electricity generating mode to the water electrolysis mode in themethod of operating the water electrolysis and electricity generatingsystem 10.

As shown in FIG. 14A, when a request is made from the VPP server 240 tothe system ECU 236 via the gateway server 238 to switch from theelectricity generating mode to the water electrolysis mode, anelectricity generation stopping step is performed (step S30). Morespecifically, as shown in FIG. 14B, in the electricity generationstopping step, the system ECU 236 switches to an open circuit voltage(OCV) condition (step S31). In particular, the system ECU 236slope-controls (decreases at a constant rate) the flow rate and the loadcurrent of the hydrogen gas and the oxygen-containing gas supplied tothe cell member 12 so as to bring about the OCV condition.

Next, when the OCV condition is brought about, the injector control unit252 stops driving the injector 168 (step S32), and the pump control unit250 stops driving the air pump 116 (step S33). Consequently, supplyingof the hydrogen gas and the oxygen-containing gas to the cell member 12is stopped.

Thereafter, a water electrolysis preparatory step is carried out (stepS34 of FIG. 14A). In the water electrolysis preparatory step, the valvecontrol unit 248 controls the various valves to place them in a secondswitching mode (step S35). More specifically, as shown in FIG. 6 , thevalve control unit 248 opens the pure water supply valve 100 and closesthe hydrogen gas supply valve 158 and the purge valve 184. Further, thevalve control unit 248 controls the flow rate control valve 128 to bringabout a flow through state of the first bypass flow path 126.Furthermore, the valve control unit 248 controls the first flow pathswitching valve 130 to bring about the flow through state of thedilution flow path 110. Further, the valve control unit 248 controls thesecond flow path switching valve 136 to bring about the flow throughstate of the downstream side lead-out flow path 84 b. Furthermore, thevalve control unit 248 controls the third flow path switching valve 194to bring about the flow through state of the dehumidifying flow path178.

Next, as shown in FIG. 15 , the pump control unit 250 drives the waterpump 94 at the rated flow rate (step S36). Upon doing so, the waterinside the first storage unit 86 is supplied to the cell member 12 viathe first supply flow path 82. The water that is led out from the cellmember 12 flows through the first lead-out flow path 84, and is returnedto the first storage unit 86.

When the water pump 94 is driven, a determination is made as to whetheror not inclusion of air (mixing of air) has occurred in the first supplyflow path 82, and first fluid flow path 44 of the cell member 12 and thefirst lead-out flow path 84. More specifically, the system ECU 236measures a closing time period t2 (valve opening interval) of the purewater regulating valve 76 (step S37). Next, the determination unit 254determines whether or not the closing time period t2 of the pure waterregulating valve 76 is greater than or equal to the predetermined timeperiod t0 (step S38). In the case that the closing time period t2 of thepure water regulating valve 76 does not reach the predetermined timeperiod t0 (step S38: NO), the process of step S37 is performed again.More specifically, in the case that the water level acquired by thefirst water level sensor LS1 is lower than the lower limit level, thepure water regulating valve 76 is opened, and therefore, the process ofstep S37 is performed again.

In the case that the closing time period t2 of the pure water regulatingvalve 76 has become greater than or equal to the predetermined timeperiod t0 (step S38: YES), then based on the water level inside thefirst storage unit 86 acquired by the first water level sensor LS1, thesystem ECU 236 calculates an amount of fluctuation ΔM in the water levelper unit time inside the first storage unit 86 (step S39). Statedotherwise, step S39 is carried out in the case that the predeterminedtime period t0 has elapsed after the water level acquired by the firstwater level sensor LS1 has reached the reference level and the purewater regulating valve 76 has been closed. Subsequently, thedetermination unit 254 makes a determination as to whether or not thecalculated amount of fluctuation ΔM in the water level lies within apredetermined amount of fluctuation ΔM0 in the water level (step S40).In the case that the calculated amount of fluctuation ΔM in the waterlevel is greater than the predetermined amount of fluctuation ΔM0 in thewater level, the processes of step S39 and thereafter are performedagain.

In the case that the calculated amount of fluctuation ΔM in the waterlevel lies within the predetermined amount of fluctuation ΔM0 in thewater level, the system ECU 236 determines that the first supply flowpath 82, and the first fluid flow path 44 of the cell member 12 and thefirst lead-out flow path 84 have been replaced with water (pure water),and a water electrolysis starting step is performed (step S41 of FIG.14A). In particular, the system ECU 236 drives the electrolytic powersource 50 and applies a voltage to the cell member 12.

The present embodiment exhibits the following advantageous effects.

The water electrolysis and electricity generating system 10 is equippedwith the first supply flow path 82, the first lead-out flow path 84, thewater introduction flow path 81, the oxygen-containing gas flow path106, the oxygen-containing gas introduction flow path 108, the firstgas-liquid separator 80, and the dilution flow path 110. The firstsupply flow path 82 is connected to the first inlet port member 56 athat communicates with the first fluid flow path 44. The first lead-outflow path 84 is connected to the first outlet port member 56 b thatcommunicates with the first fluid flow path 44, and at the time of thewater electrolysis mode, the gas-containing water containing the producthydrogen gas is led out. The water introduction flow path 81 introducesthe water into the first supply flow path 82. The oxygen-containing gasflows through the oxygen-containing gas flow path 106. Theoxygen-containing gas introduction flow path 108 introduces theoxygen-containing gas that flows through the oxygen-containing gas flowpath 106 into the first supply flow path 82. The first gas-liquidseparator 80 separates into a gas and a liquid the gas-containing waterthat is guided from the first lead-out flow path 84. The dilution flowpath 110 guides the oxygen-containing gas that flows through theoxygen-containing gas flow path 106 to the first gas-liquid separator 80as a diluting gas.

In accordance with such a configuration, at the time of the waterelectrolysis mode, the water can be supplied from the water introductionflow path 81 to the first inlet port member 56 a via the first supplyflow path 82, and at the time of the electricity generating mode, theoxygen-containing gas can be supplied from the oxygen-containing gasflow path 106 to the first inlet port member 56 a via theoxygen-containing gas introduction flow path 108 and the first supplyflow path 82. More specifically, the first supply flow path 82 servesboth as a flow path for supplying water and a flow path for supplyingthe oxygen-containing gas. A more compact configuration is broughtabout, in comparison with a case in which each of the water supply flowpath and the oxygen-containing gas supply flow path are connectedrespectively to the cell member 12.

Further, the oxygen-containing gas that flows through theoxygen-containing gas flow path 106 at the time of the waterelectrolysis mode can also be used as a diluting gas for the firstgas-liquid separator 80. Consequently, a more compact configuration canbe brought about, compared with a case in which a device for supplyingthe oxygen-containing gas to the cell member 12, and a device forsupplying the diluting gas to the first gas-liquid separator 80 areseparately provided. Thus, the water electrolysis and electricitygenerating system 10 can be made smaller in scale, together withenabling a reduction in the manufacturing cost of the system by a simpleconfiguration.

The water electrolysis and electricity generating system 10 is equippedwith the first flow path switching valve 130 that is capable ofswitching between the flow through state of the oxygen-containing gasintroduction flow path 108 and the flow through state of the dilutionflow path 110. The flow through state of the oxygen-containing gasintroduction flow path 108 is a state in which the flow of theoxygen-containing gas from the oxygen-containing gas flow path 106 tothe oxygen-containing gas introduction flow path 108 is permitted,together with blocking the flow of the oxygen-containing gas from theoxygen-containing gas flow path 106 to the dilution flow path 110. Theflow through state of the dilution flow path 110 is a state in which theflow of the oxygen-containing gas from the oxygen-containing gas flowpath 106 to the oxygen-containing gas introduction flow path 108 isblocked, together with permitting the flow of the oxygen-containing gasfrom the oxygen-containing gas flow path 106 to the dilution flow path110.

In accordance with such a configuration, at the time of the waterelectrolysis mode, by the first flow path switching valve 130 beingoperated to bring about the flow through state of the dilution flow path110, the oxygen-containing gas can be introduced into the firstgas-liquid separator 80. Further, at the time of the electricitygenerating mode, by the first flow path switching valve 130 beingoperated to bring about the flow through state of the oxygen-containinggas introduction flow path 108, the oxygen-containing gas can beintroduced into the cell member 12.

Only one air pump 116 is installed in the oxygen-containing gas flowpath 106. At the time of the water electrolysis mode, theoxygen-containing gas discharged from the air pump 116 is guided to thefirst gas-liquid separator 80 via the dilution flow path 110. At thetime of the electricity generating mode, the oxygen-containing gasdischarged from the air pump 116 is guided to the first fluid flow path44 of the cell member 12 via the oxygen-containing gas introduction flowpath 108 and the first supply flow path 82.

In accordance with such a configuration, the oxygen-containing gas thatis used for generating electricity, and the oxygen-containing gas thatis used for dilution can be supplied by one air pump 116. Therefore, byusing the devices in common, it is possible to reduce costs.

The water electrolysis and electricity generating system 10 is equippedwith the heating medium circulation flow path 142 and the heating mediumpump 144. A heating medium flows through the heating medium circulationflow path 142. The heating medium pump 144 causes the heating medium tobe circulated through the heating medium circulation flow path 142. Thefirst heat exchanger 96 and the second heat exchanger 122 are installedin the heating medium circulation flow path 142. The first heatexchanger 96 carries out heat exchange between the water that flowsthrough the water introduction flow path 81 and the heating medium. Thesecond heat exchanger 122 carries out heat exchange between theoxygen-containing gas that flows through the oxygen-containing gas flowpath 106 and the heating medium.

In accordance with such a configuration, since heat exchange is carriedout by the first heat exchanger 96 between the water that flows throughthe water introduction flow path 81 and the heating medium (in the firstheat exchanger 96, the water that flows through the water introductionflow path 81 does not carry out heat exchange directly with the exteriorair), even in the case that the exterior air is below the freezingpoint, it is possible to prevent the water in the water introductionflow path 81 from freezing. Further, since the heating medium thatreceives heat from the oxygen-containing gas at the second heatexchanger 122 circulates in the heating medium circulation flow path142, it is possible to further suppress freezing of the water in thewater introduction flow path 81.

The heating medium radiator 146 in order to cool the heating medium isinstalled in the heating medium circulation flow path 142. The heatingmedium that is led out from the heating medium radiator 146, afterhaving flowed sequentially in this order through the second heatexchanger 122 and the first heat exchanger 96, is returned to theheating medium radiator 146.

In accordance with such a configuration, the oxygen-containing gas thatflows through the oxygen-containing gas flow path 106 can be efficientlycooled by the second heat exchanger 122. Further, in the case that theexterior air is below the freezing point, the heating medium, which hasreceived heat from the oxygen-containing gas at the second heatexchanger 122, flows through the first heat exchanger 96 before beingguided to the heating medium radiator 146. Therefore, freezing of thewater in the water introduction flow path 81 can be further suppressed.

The humidifier 124 in order to humidify the oxygen-containing gas isinstalled on a more downstream side than the second heat exchanger 122in the oxygen-containing gas flow path 106. In the humidifier 124, atthe time of the electricity generating mode, the oxygen-containing gasis humidified by the oxygen containing exhaust gas that is led out fromthe first outlet port member 56 b.

In accordance with such a configuration, the oxygen-containing gas,which is temperature-controlled (cooled) by the second heat exchanger122, is guided to the humidifier 124. Therefore, even if theoxygen-containing gas, which has been raised in temperature by the cellmember 12 at the time of the electricity generating mode, flows throughthe humidifier 124, it is possible to prevent the temperature and thehumidity of the oxygen-containing gas that is introduced into the cellmember 12 from rising excessively.

The first bypass flow path 126 and the flow rate control valve 128 areinstalled in the oxygen-containing gas flow path 106. The first bypassflow path 126 is connected to the upstream side of the humidifier 124and the downstream side of the humidifier 124 to detour around thehumidifier 124. The flow rate control valve 128 is capable of adjustingthe ratio between the flow rate of the oxygen-containing gas that isguided to the humidifier 124 and the flow rate of the oxygen-containinggas that is guided to the first bypass flow path 126.

In accordance with such a configuration, at the time of switching fromthe water electrolysis mode to the electricity generating mode, thedried oxygen-containing gas, which has flowed through the first bypassflow path 126, can be introduced into the cell member 12. Therefore, thewater drainage process (purging process) of the residual water remainingin the first fluid flow path 44 of the cell member 12 can be efficientlyperformed.

The water electrolysis and electricity generating system 10 is equippedwith the second supply flow path 154, the second lead-out flow path 170,the second gas-liquid separator 172, the hydrogen exhaust gascirculation flow path 176, and the storage flow path 180. The secondsupply flow path 154 supplies the hydrogen gas to the second fluid flowpath 46. At the time of the water electrolysis mode, the producthydrogen gas is led out from the second fluid flow path 46, and further,at the time of the electricity generating mode, the hydrogen exhaust gasis led out from the second fluid flow path 46 into the second lead-outflow path 170. The second gas-liquid separator 172 separates into a gasand a liquid the product hydrogen gas and the hydrogen exhaust gas whichhave been guided from the second lead-out flow path 170. The hydrogenexhaust gas circulation flow path 176 guides the hydrogen exhaust gas,which has been separated into a gas and a liquid by the secondgas-liquid separator 172, to the second supply flow path 154. Thestorage flow path 180 guides the product hydrogen gas, which has beenseparated into a gas and a liquid by the second gas-liquid separator172, to the hydrogen storage unit 410. In the water electrolysis andelectricity generating system 10, the second lead-out flow path 170 andthe second gas-liquid separator 172 are shared in common by the waterelectrolysis mode and the electricity generating mode.

In accordance with such a configuration, since the second lead-out flowpath 170 and the second gas-liquid separator 172 are shared in common bythe water electrolysis mode and the electricity generating mode, thereis no need to separately provide a lead-out flow path and a gas-liquidseparator for use by the water electrolysis mode, and a lead-out flowpath and a gas-liquid separator for use by the electricity generatingmode. Therefore, the water electrolysis and electricity generatingsystem 10 can be made smaller in scale, together with enabling areduction in the manufacturing cost of the system by a simpleconfiguration.

The water electrolysis and electricity generating system 10 is equippedwith the intermediate lead-out flow path 174, the dehumidifying flowpath 178, and the second flow path switching valve 136. The producthydrogen gas and the hydrogen exhaust gas, which have flowed through thesecond gas-liquid separator 172, are led out to the intermediatelead-out flow path 174. The dehumidifying flow path 178 dehumidifies theproduct hydrogen gas that flows through the intermediate lead-out flowpath 174, and guides the dehumidified hydrogen gas to the storage flowpath 180. The second flow path switching valve 136 is capable ofswitching between a flow through state of the dehumidifying flow path178 and a flow through state of the hydrogen exhaust gas circulationflow path 176. The flow through state of the dehumidifying flow path 178is a state in which the flow of the hydrogen exhaust gas from theintermediate lead-out flow path 174 to the hydrogen exhaust gascirculation flow path 176 is permitted, together with blocking the flowof the hydrogen exhaust gas from the intermediate lead-out flow path 174to the dehumidifying flow path 178. The flow through state of thehydrogen exhaust gas circulation flow path 176 is a state in which theflow of the product hydrogen gas from the intermediate lead-out flowpath 174 to the dehumidifying flow path 178 is permitted, together withblocking the flow of the product hydrogen gas from the intermediatelead-out flow path 174 to the hydrogen exhaust gas circulation flow path176.

In accordance with such a configuration, at the time of the waterelectrolysis mode, by the second flow path switching valve 136 beingoperated to bring about the flow through state of the dehumidifying flowpath 178, the product hydrogen gas that is led out from the secondgas-liquid separator 172 to the intermediate lead-out flow path 174 canbe guided to the hydrogen storage unit 410 via the dehumidifying flowpath 178 and the storage flow path 180. Further, at the time of theelectricity generating mode, by the second flow path switching valve 136being operated to bring about the flow through state of the hydrogenexhaust gas circulation flow path 176, the hydrogen exhaust gas that isled out from the second gas-liquid separator 172 to the intermediatelead-out flow path 174 can be introduced into the cell member 12 via thehydrogen exhaust gas circulation flow path 176 and the second supplyflow path 154.

The first dehumidifying adsorption unit 200 a, the second dehumidifyingadsorption unit 200 b, and the dehumidification switching unit 202 areinstalled in the dehumidifying flow path 178. The first dehumidifyingadsorption unit 200 a and the second dehumidifying adsorption unit 200 bare capable of dehumidifying the product hydrogen gas and restoring thedehumidifying function thereof. The dehumidification switching unit 202switches the direction in which the product hydrogen gas flows, in amanner so that the order in which the product hydrogen gas flows throughthe first dehumidifying adsorption unit 200 a and the seconddehumidifying adsorption unit 200 b is changed.

In accordance with such a configuration, at the time of the waterelectrolysis mode, the first dehumidifying adsorption unit 200 a and thesecond dehumidifying adsorption unit 200 b can undergoself-regeneration. Therefore, the replacement interval of the firstdehumidifying adsorption unit 200 a and the second dehumidifyingadsorption unit 200 b can be prolonged.

The water electrolysis and electricity generating system 10 is equippedwith the supply and discharge flow path 150. The supply and dischargeflow path 150 leads the product hydrogen gas in the storage flow path180 out to the hydrogen storage unit 410. Further, the supply anddischarge flow path 150 introduces the hydrogen gas in the hydrogenstorage unit 410 into the second supply flow path 154. The gas meter234, which acquires the flow rate of the hydrogen gas from the hydrogenstorage unit 410 to the supply and discharge flow path 150 and the flowrate of the product hydrogen gas from the supply and discharge flow path150 to the hydrogen storage unit 410, is installed in the supply anddischarge flow path 150.

In accordance with such a configuration, due to the information acquiredby the gas meter 234, the amount of the hydrogen gas that is introducedand the amount of the product hydrogen gas that is led out can be easilycontrolled.

The method of operating the water electrolysis and electricitygenerating system 10 includes, at the time of switching from the waterelectrolysis mode to the electricity generating mode, the waterelectrolysis stopping step, the purging step, and the electricitygeneration starting step. In the water electrolysis stopping step, thewater electrolysis by the cell member 12 is stopped. In the purgingstep, after the water electrolysis stopping step, the oxygen-containinggas is supplied from the oxygen-containing gas flow path 106 to thefirst fluid flow path 44 via the oxygen-containing gas introduction flowpath 108, the first supply flow path 82, and the first inlet port member56 a. In the electricity generation starting step, after the purgingstep, the cell member 12 is made to generate electricity based on thepredetermined required load value.

In accordance with such a method, by the purging step, at the time ofthe water electrolysis mode, the water (residual water) existing in thefirst supply flow path 82 and the first fluid flow path 44 of the cellmember 12 can be drained into the first gas-liquid separator 80 by theoxygen-containing gas. Consequently, it is possible to smoothly andreliably carry out switching from the water electrolysis mode to theelectricity generating mode. Further, since a portion of the firstsupply flow path 82 is used as the water supply flow path and the purgeflow path, the water electrolysis and electricity generating system 10can be made smaller in scale, together with enabling a reduction in themanufacturing cost of the system.

In the purging step, the first electrode 30 is dried by theoxygen-containing gas that flows through the first fluid flow path 44.

In accordance with such a method, the generation of electricity by thecell member 12 can be smoothly started in the electricity generationstarting step.

The humidifier 124 and the first bypass flow path 126 are installed inthe oxygen-containing gas flow path 106. The humidifier 124 humidifiesthe oxygen-containing gas. The first bypass flow path 126 is connectedto an upstream side and a downstream side of the humidifier 124 in theoxygen-containing gas flow path 106 to detour around the humidifier 124.In the purging step, the oxygen-containing gas is allowed to flowthrough the first bypass flow path 126 without being allowed to flowthrough the humidifier 124.

In accordance with such a method, the first electrode 30 can beefficiently dried during the purging step.

The cell member 12 includes the plurality of cells 20. The method ofoperating the water electrolysis and electricity generating system 10includes the electricity generation preparatory step, which is performedbetween the purging step and the electricity generation starting step.In the electricity generation preparatory step, the cell member 12 ismade to generate electricity under the low load condition which is lowerthan the required load value, and the cell voltage of each of the cells20 is acquired. The electricity generation starting step is carried outin the case that each of the cell voltages acquired in the electricitygeneration preparatory step has reached a value of greater than or equalto the predetermined value.

In accordance with such a method, each of the cells 20 can reliably bemade to generate electricity in the electricity generation startingstep.

In the electricity generation preparatory step, a determination is madeas to whether or not a deviation in the cell voltage of the plurality ofcells 20 resides within a predetermined range. The electricitygeneration starting step is carried out in the case that the deviationin the cell voltage lies within the predetermined range in theelectricity generation preparatory step.

In accordance with such a method, in the electricity generation startingstep, each of the cells 20 can be made to generate electricity in awell-balanced manner.

The method of operating the water electrolysis and electricitygenerating system 10 includes, at the time of switching from theelectricity generating mode to the water electrolysis mode, theelectricity generation stopping step and the water electrolysis startingstep. In the electricity generation stopping step, the generation ofelectricity in the cell member 12 is stopped. In the water electrolysisstarting step, in the case that the water level inside the firstgas-liquid separator 80 is greater than or equal to the lower limitlevel, the water electrolysis of the cell member 12 is initiated.

In accordance with such a method, since water electrolysis is initiatedin the case that the water level in the first gas-liquid separator 80 isgreater than or equal to the lower limit level, it is possible tosuppress mixing of air into the water that is supplied to the cellmember 12 at the time of the water electrolysis starting step.Consequently, it is possible to smoothly carry out switching from theelectricity generating mode to the water electrolysis mode.

In the water electrolysis starting step, in the case that the amount offluctuation ΔM in the water level per unit time inside the firstgas-liquid separator 80 is less than or equal to the predeterminedamount of fluctuation ΔM0 in the water level, the water electrolysis ofthe cell member 12 is initiated.

In accordance with such a method, it is possible to further suppress themixing of air into the water that is supplied to the cell member 12 atthe time of the water electrolysis starting step.

The number of dehumidifying and adsorption units of the waterelectrolysis and electricity generating system 10 is not limited to two,and may be three or more.

The present invention is not limited to the embodiment described above,and it goes without saying that various modified or additionalconfigurations could be adopted therein without departing from theessence and gist of the present invention.

The embodiment described above can be summarized in the followingmanner.

In the above-described embodiment, there is disclosed the waterelectrolysis and electricity generating system (10) comprising the cellmember (12) having the MEA (22) in which the electrolyte membrane (28)is sandwiched between the first electrode (30) and the second electrode(32), the first fluid flow path (44) that supplies the water and theoxygen-containing gas to the first electrode, and the second fluid flowpath (46) that supplies the hydrogen gas to the second electrode,wherein the water electrolysis and electricity generating system iscapable of being switched between the water electrolysis mode, in whichthe water supplied to the first electrode is electrolyzed to therebygenerate product hydrogen gas at the second electrode, and theelectricity generating mode, in which electricity is generated by anelectrochemical reaction that takes place between the oxygen-containinggas supplied to the first electrode and the hydrogen gas supplied to thesecond electrode, the water electrolysis and electricity generatingsystem further comprising the supply flow path (82) connected to theinlet port member (56 a) that communicates with the first fluid flowpath, the lead-out flow path (84) connected to the outlet port member(56 b) that communicates with the first fluid flow path and from whichthe gas-containing water containing the product hydrogen gas is led outat the time of the water electrolysis mode, the water introduction flowpath (81) through which the water is introduced into the supply flowpath, the oxygen-containing gas flow path (106) through which theoxygen-containing gas flows, the oxygen-containing gas introduction flowpath (108) which introduces the oxygen-containing gas that flows throughthe oxygen-containing gas flow path into the supply flow path, thegas-liquid separator (80) that separates into a gas and a liquid thegas-containing water that is guided from the lead-out flow path, and thedilution flow path (110) that guides the oxygen-containing gas thatflows through the oxygen-containing gas flow path to the gas-liquidseparator as a diluting gas.

In the above-described water electrolysis and electricity generatingsystem, there may further be provided the flow path switching valve(130) that is capable of switching between a state in which the flow ofthe oxygen-containing gas from the oxygen-containing gas flow path tothe oxygen-containing gas introduction flow path is permitted, togetherwith blocking the flow of the oxygen-containing gas from theoxygen-containing gas flow path to the dilution flow path, and a statein which the flow of the oxygen-containing gas from theoxygen-containing gas flow path to the oxygen-containing gasintroduction flow path is blocked, together with permitting the flow ofthe oxygen-containing gas from the oxygen-containing gas flow path tothe dilution flow path.

In the above-described water electrolysis and electricity generatingsystem, only one air pump (116) may be installed in theoxygen-containing gas flow path, wherein at the time of the waterelectrolysis mode, the oxygen-containing gas discharged from the airpump may be guided to the gas-liquid separator through the dilution flowpath, and at the time of the electricity generating mode, theoxygen-containing gas may be guided to the first fluid flow path of thecell member via the oxygen-containing gas introduction flow path and thesupply flow path.

In the above-described water electrolysis and electricity generatingsystem, there may further be provided the heating medium circulationflow path (142) through which the heating medium flows, and the heatingmedium pump (144) in order to cause the heating medium to be circulatedin the heating medium circulation flow path, wherein the first heatexchanger (96) that carries out heat exchange between the water thatflows through the water introduction flow path and the heating medium,and the second heat exchanger (122) that carries out heat exchangebetween the oxygen-containing gas that flows through theoxygen-containing gas flow path and the heating medium may be installedin the heating medium circulation flow path.

In the above-described water electrolysis and electricity generatingsystem, a heating medium radiator (146) in order to cool the heatingmedium may be installed in the heating medium circulation flow path, andthe heating medium that is led out from the heating medium radiator maybe returned to the heating medium radiator after having flowedsequentially in this order through the second heat exchanger and thefirst heat exchanger.

In the above-described water electrolysis and electricity generatingsystem, the humidifier (124) in order to humidify the oxygen-containinggas may be installed in the oxygen-containing gas flow path on a moredownstream side than the second heat exchanger, and in the humidifier,at the time of the electricity generating mode, the oxygen-containinggas may be humidified by the oxygen containing exhaust gas that is ledout from the outlet port member.

In the above-described water electrolysis and electricity generatingsystem, the bypass flow path (126), which is connected to the upstreamside of the humidifier and the downstream side of the humidifier todetour around the humidifier, and the flow rate control valve (128),which is capable of adjusting a ratio between the flow rate of theoxygen-containing gas that is guided to the humidifier and the flow rateof the oxygen-containing gas that is guided to the bypass flow path, maybe installed in the oxygen-containing gas flow path.

In the above-described embodiment, there is disclosed the waterelectrolysis and electricity generating system comprising the cellmember having the MEA in which the electrolyte membrane is sandwichedbetween the first electrode and the second electrode, the first fluidflow path that supplies the water and the oxygen-containing gas to thefirst electrode, and the second fluid flow path that supplies thehydrogen gas to the second electrode, wherein the water electrolysis andelectricity generating system is capable of being switched between thewater electrolysis mode, in which the water supplied to the firstelectrode is electrolyzed to thereby generate product hydrogen gas atthe second electrode, and the electricity generating mode, in whichelectricity is generated by an electrochemical reaction that takes placebetween the oxygen-containing gas supplied to the first electrode andthe hydrogen gas supplied to the second electrode, the waterelectrolysis and electricity generating system further comprising thesupply flow path (154) that supplies the hydrogen gas to the secondfluid flow path, the lead-out flow path (170) through which the producthydrogen gas is led out from the second fluid flow path at a time of thewater electrolysis mode, and through which the hydrogen exhaust gas isled out from the second fluid flow path at a time of the electricitygenerating mode, the gas-liquid separator (172) that separates into agas and a liquid the product hydrogen gas and the hydrogen exhaust gasthat are led out from the lead-out flow path, the circulation flow path(176) that guides the hydrogen exhaust gas, which has been separatedinto a gas and a liquid by the gas-liquid separator, to the supply flowpath, and the storage flow path (180) that guides the product hydrogengas, which has been separated into a gas and a liquid by the gas-liquidseparator, to the hydrogen storage unit (410), wherein the lead-out flowpath and the gas-liquid separator are shared in common by the hydrogenelectrolysis mode and the electricity generating mode.

In the above-described water electrolysis and electricity generatingsystem, there may further be provided the intermediate lead-out flowpath (174) from which the product hydrogen gas and the hydrogen exhaustgas that have flowed through the gas-liquid separator are led out, thedehumidifying flow path (178) that dehumidifies the product hydrogen gasthat flows through the intermediate lead-out flow path, and guides theproduct hydrogen gas to the storage flow path, and the flow pathswitching valve (194) that is capable of switching between a state inwhich, at the time of the water electrolysis mode, flow of the hydrogenexhaust gas from the intermediate lead-out flow path to the circulationflow path is permitted, together with blocking flow of the hydrogenexhaust gas from the intermediate lead-out flow path to thedehumidifying flow path, and a state in which, at the time of theelectricity generating mode, flow of the product hydrogen gas from theintermediate lead-out flow path to the dehumidifying flow path ispermitted, together with blocking flow of the product hydrogen gas fromthe intermediate lead-out flow path to the circulation flow path.

In the above-described water electrolysis and electricity generatingsystem, in the dehumidifying flow path, there may be installed theplurality of dehumidifying adsorption units (200 a, 200 b) which arecapable of dehumidifying the product hydrogen gas and restoring thedehumidifying function thereof, and the dehumidification switching unit(202) that switches a direction through which the product hydrogen gasflows, in a manner so that an order in which the product hydrogen gasflows through the plurality of dehumidifying adsorption units ischanged.

In the above-described water electrolysis and electricity generatingsystem, there may further be provided the supply and discharge flow path(150) in order to lead out the product hydrogen gas in the storage flowpath to the hydrogen storage unit, and to introduce the hydrogen gas inthe hydrogen storage unit into the supply flow path, wherein, in thesupply and discharge flow path, there is installed the flow rateacquisition unit (234) that acquires the flow rate of the hydrogen gasfrom the hydrogen storage unit to the supply and discharge flow path,and the flow rate of the product hydrogen gas from the supply anddischarge flow path to the hydrogen storage unit.

In the above-described embodiment, there is disclosed the method ofoperating the water electrolysis and electricity generating systemcomprising the cell member having the MEA in which the electrolytemembrane is sandwiched between the first electrode and the secondelectrode, the first fluid flow path that supplies the water and theoxygen-containing gas to the first electrode, and the second fluid flowpath that supplies the hydrogen gas to the second electrode, wherein thewater electrolysis and electricity generating system is capable of beingswitched between the water electrolysis mode, in which the watersupplied to the first electrode is electrolyzed to thereby generateproduct hydrogen gas at the second electrode, and the electricitygenerating mode, in which electricity is generated by an electrochemicalreaction that takes place between the oxygen-containing gas supplied tothe first electrode and the hydrogen gas supplied to the secondelectrode, the water electrolysis and electricity generating systemfurther comprising the supply flow path connected to the inlet portmember that communicates with the first fluid flow path, the lead-outflow path connected to the outlet port member that communicates with thefirst fluid flow path and from which the gas-containing water containingthe product hydrogen gas is led out at the time of the waterelectrolysis mode, the water introduction flow path through which thewater is introduced into the supply flow path, the oxygen-containing gasflow path through which the oxygen-containing gas flows, theoxygen-containing gas introduction flow path which introduces theoxygen-containing gas that flows through the oxygen-containing gas flowpath into the supply flow path, and the gas-liquid separator thatseparates into a gas and a liquid the gas-containing water that isguided from the lead-out flow path, the method of operating the waterelectrolysis and electricity generating system comprising, at a time ofswitching from the water electrolysis mode to the electricity generatingmode, the water electrolysis stopping step of stopping the waterelectrolysis by the cell member, after the water electrolysis stoppingstep, the purging step of causing the oxygen-containing gas to flow fromthe oxygen-containing gas flow path to the gas-liquid separator via theoxygen-containing gas introduction flow path, the supply flow path, theinlet port member, the first fluid flow path, the outlet port member,and the lead-out flow path, and after the purging step, the electricitygeneration starting step of causing the cell member to generateelectricity based on the predetermined required load value.

In the above-described method of operating the water electrolysis andelectricity generating system, in the purging step, the first electrodemay be dried by the oxygen-containing gas that flows through the firstfluid flow path.

In the above-described method of operating the water electrolysis andelectricity generating system, the humidifier in order to humidify theoxygen-containing gas, and the bypass flow path, which is connected tothe upstream side of the humidifier and the downstream side of thehumidifier to detour around the humidifier, may be installed in theoxygen-containing gas flow path, and in the purging step, theoxygen-containing gas may be made to flow through the bypass flow pathwithout flowing through the humidifier.

In the above-described method of operating the water electrolysis andelectricity generating system, the cell member may include a pluralityof cells, there may further be provided the electricity generatingpreparatory step, which is performed after the purging step and prior tothe electricity generation starting step, and in the electricitygenerating preparatory step, the cell member may be made to generateelectricity under a low load condition that is lower than the requiredload value, each of the cell voltages of the cells may be acquired, andthe electricity generation starting step may be implemented in the casethat aforementioned each of the cell voltages acquired in theelectricity generation preparatory step has reached a value that isgreater than or equal to the predetermined value.

In the above-described method of operating the water electrolysis andelectricity generating system, in the electricity generating preparatorystep, it may be determined whether or not a deviation of the cellvoltages of the plurality of cells lies within a predetermined range,and the electricity generation starting step may be implemented in thecase that the deviation of the cell voltages lies within thepredetermined range in the electricity generation preparatory step.

In the above-described embodiment, there is disclosed the method ofoperating the water electrolysis and electricity generating systemcomprising the cell member having the MEA in which the electrolytemembrane is sandwiched between the first electrode and the secondelectrode, the first fluid flow path that supplies the water and theoxygen-containing gas to the first electrode, and the second fluid flowpath that supplies the hydrogen gas to the second electrode, wherein thewater electrolysis and electricity generating system is capable of beingswitched between the water electrolysis mode, in which the watersupplied to the first electrode is electrolyzed to thereby generateproduct hydrogen gas at the second electrode, and the electricitygenerating mode, in which electricity is generated by theelectrochemical reaction that takes place between the oxygen-containinggas supplied to the first electrode and the hydrogen gas supplied to thesecond electrode, the water electrolysis and electricity generatingsystem further comprising the water introduction flow path whichsupplies the water to the inlet port member that communicates with thefirst fluid flow path, the lead-out flow path connected to the outletport member that communicates with the first fluid flow path and fromwhich the gas-containing water containing the product hydrogen gas isled out at the time of the water electrolysis mode, and the gas-liquidseparator, which is formed to be capable of storing the water thereintogether with the water introduction flow path being connected thereto,and to gas-liquid separate the gas-containing water that is guided fromthe lead-out flow path, wherein the method of operating the waterelectrolysis and electricity generating system comprises, at the time ofswitching from the electricity generating mode to the water electrolysismode, an electricity generation stopping step of stopping the generationof electricity by the cell member, and a water electrolysis startingstep of starting water electrolysis by the cell member in the case thatthe water level inside the gas-liquid separator is greater than or equalto the lower limit level.

In the above-described method of operating the water electrolysis andelectricity generating system, in the water electrolysis starting step,in the case that the amount of fluctuation in the water level per unittime inside the gas-liquid separator is less than or equal to apredetermined fluctuation in the water level, the water electrolysis ofthe cell member may be initiated.

What is claimed is:
 1. A method of operating a water electrolysis andelectricity generating system comprising a cell member having a membraneelectrode assembly in which an electrolyte membrane is sandwichedbetween a first electrode and a second electrode, a first fluid flowpath configured to supply water and an oxygen-containing gas to thefirst electrode, and a second fluid flow path configured to supplyhydrogen gas to the second electrode; wherein the water electrolysis andelectricity generating system is configured to be capable of beingswitched between a water electrolysis mode, in which the water suppliedto the first electrode is electrolyzed to thereby generate producthydrogen gas at the second electrode, and an electricity generatingmode, in which electricity is generated by an electrochemical reactionthat takes place between the oxygen-containing gas supplied to the firstelectrode and the hydrogen gas supplied to the second electrode; thewater electrolysis and electricity generating system further comprises:a supply flow path connected to an inlet port member configured tocommunicate with the first fluid flow path; a lead-out flow pathconnected to an outlet port member configured to communicate with thefirst fluid flow path and from which a gas-containing water containingthe product hydrogen gas is led out at the time of the waterelectrolysis mode; a water introduction flow path configured tointroduce the water into the supply flow path; an oxygen-containing gasflow path through which the oxygen-containing gas flows; anoxygen-containing gas introduction flow path configured to introduce theoxygen-containing gas that flows through the oxygen-containing gas flowpath into the supply flow path; and a gas-liquid separator configured toseparate into a gas and a liquid the gas-containing water that is guidedfrom the lead-out flow path, the method of operating the waterelectrolysis and electricity generating system comprising at a time ofswitching from the water electrolysis mode to the electricity generatingmode: a water electrolysis stopping step of stopping the waterelectrolysis at the cell member, after the water electrolysis stoppingstep, a purging step of causing the oxygen-containing gas to flow fromthe oxygen-containing gas flow path to the gas-liquid separator via theoxygen-containing gas introduction flow path, the supply flow path, theinlet port member, the first fluid flow path, the outlet port member,and the lead-out flow path; and after the purging step, an electricitygeneration starting step of causing the cell member to generateelectricity based on a predetermined required load value.
 2. The methodof operating the water electrolysis and electricity generating systemaccording to claim 1, wherein in the purging step, the first electrodeis dried by the oxygen-containing gas that flows through the first fluidflow path.
 3. The method of operating the water electrolysis andelectricity generating system according to claim 2, wherein a humidifierconfigured to humidify the oxygen-containing gas, and a bypass flowpath, which is connected to an upstream side of the humidifier and adownstream side of the humidifier to detour around the humidifier, areinstalled in the oxygen-containing gas flow path, and in the purgingstep, the oxygen-containing gas is made to flow through the bypass flowpath without flowing through the humidifier.
 4. The method of operatingthe water electrolysis and electricity generating system according toclaim 1, wherein the cell member includes a plurality of cells, themethod further comprising an electricity generating preparatory step,which is performed after the purging step and prior to the electricitygeneration starting step, wherein in the electricity generatingpreparatory step, the cell member is made to generate electricity undera low load condition that is lower than a required load value, and eachof cell voltages of the cells is acquired, and the electricitygeneration starting step is implemented in a case that aforementionedeach of the cell voltages acquired in the electricity generationpreparatory step has reached a value that is greater than or equal to apredetermined value.
 5. The method of operating the water electrolysisand electricity generating system according to claim 4, wherein in theelectricity generating preparatory step, it is determined whether or nota deviation of the cell voltages of the plurality of cells lies within apredetermined range, and the electricity generation starting step isimplemented in a case that the deviation of the cell voltages lieswithin the predetermined range in the electricity generation preparatorystep.
 6. A method of operating a water electrolysis and electricitygenerating system comprising a cell member having a membrane electrodeassembly in which an electrolyte membrane is sandwiched between a firstelectrode and a second electrode, a first fluid flow path configured tosupply water and an oxygen-containing gas to the first electrode, and asecond fluid flow path configured to supply hydrogen gas to the secondelectrode; wherein the water electrolysis and electricity generatingsystem is configured to be capable of being switched between a waterelectrolysis mode, in which the water supplied to the first electrode iselectrolyzed to thereby generate product hydrogen gas at the secondelectrode, and an electricity generating mode, in which electricity isgenerated by an electrochemical reaction that takes place between theoxygen-containing gas supplied to the first electrode and the hydrogengas supplied to the second electrode; the water electrolysis andelectricity generating system further comprises: a supply flow pathconnected to an inlet port member configured to communicate with thefirst fluid flow path; a lead-out flow path connected to an outlet portmember configured to communicate with the first fluid flow path and fromwhich a gas-containing water containing the product hydrogen gas haspermeated from the second electrode to the first electrode and is ledout at the time of the water electrolysis mode; a water introductionflow path configured to introduce the water into the supply flow path;an oxygen-containing gas flow path through which the oxygen-containinggas flows; an oxygen-containing gas introduction flow path connected tothe oxygen-containing gas flow path and the supply flow path andconfigured to introduce the oxygen-containing gas that flows through theoxygen-containing gas flow path into the supply flow path; and agas-liquid separator configured to separate into a gas and a liquid thegas-containing water that is guided from the lead-out flow path, themethod of operating the water electrolysis and electricity generatingsystem comprising at a time of switching from the water electrolysismode to the electricity generating mode: a water electrolysis stoppingstep of stopping the water electrolysis at the cell member, after thewater electrolysis stopping step, a purging step of causing theoxygen-containing gas to flow from the oxygen-containing gas flow pathto the gas-liquid separator via the oxygen-containing gas introductionflow path, the supply flow path, the inlet port member, the first fluidflow path, the outlet port member, and the lead-out flow path; and afterthe purging step, an electricity generation starting step of causing thecell member to generate electricity based on a predetermined requiredload value.